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TWENTIETH CENTURY TEXT-BOOKS

CARL WILHELM BCIIEELE
& OermMi)', 11*2. D. ITSe.

TWENTIETH CENTURY TEXT-BOOKS

INDUCTIVE CHEMISTRY

ROBERT H. BRADBURY, A.M., Ph.D.

HEAD OF THE DEPARTMENT OF SCIENCE,
SOUTHERN HIGH SCHOOL, PHILADELPHIA

" De grandes questions restent k r6soudre,
et cette chimie min^rale, que Ton croyait
6puis6e, n'est qu'k son aurore."

Henbi Moissan.

D. APPLETON AND COMPANY

NEW YORK CHICAGO

1912

p»:juc:ai ION OH^"*^,

- J

PREFACE

In Chemistry, as in other sciences, there are, in the main, two
things to be considered — ^method and results. There is an enor-
mous mass of facts from which we have to select the indispensable
things for the beginner, and there is the general procedure or
method by which those facts have been ascertained. This book
attempts to teach the method of the science along with the facts,
and to unify the facts and logically connect them by means of the
method. It is hoped that the student who has read it will not only
know something about the subject but will know how he knows it —
that he will be able to give the evidence on which his beliefs are
based. The chapter on the atmosphere furnishes a good illustration
of the working out of this principle. The composition of the atmos-
phere is regarded as a problem. A beginning is made by utilizing
the information which the student already possesses. This leaves
him face to face with questions which can only be answered by
experiments. The discussion of these leads to new questions, which
suggest other experiments and so on until the desired result it
obtained.

Anyone who desires to do so can easily satisfy himself that this
plan possesses great advantages over the dogmatic procedure. No
originality is claimed for it, for it is simply the inductive method
employed by a large and increasing number of teachers. It will
be clear that an essential feature of the plan is a constant effort to
dovetail the facts of the science with the facts of every-day Ufe in
such a way that the student at no time gets the impression that he
has attacked something quite foreign to his ordinary experience.
Thus, the systematic classification of the elements, which completely
determines the order of topics in a work of reference, should only
be allowed a subordinate influence upon the arrangement of an
elementary text.

The book is not an abbreviated college text, nor a handbook

j subjected to hydraulic compression. The subject-matter has been

regarded from the standpoint of the student and nothing has been

J>4 4:Hi6

vi PREFACE

admitted which does not further, in some way, the orderly develop-
ment of his ideas. More space than is usual has been given to the
practical appHcations of the subject: at the same time the logical
connecting structure which has produced the applications, just as
a tree produces its fruit, has not been slighted. Special care has
been taken to bring the technology abreast of modem practice.

However, a book may be thoroughly modem and exact, on the
purely scientific side, and yet prove a complete failure in the class-
room, because it is not fitted to the needs of the student. It does
the student less damage to put into his hands a clear account of
the chemistry of two or three decades ago than to give him an abso-
lutely modem book which he cannot comprehend. There is but
one certain method of avoiding the danger of becoming unintelligible
to the beginner, namely, to try out every chapter over and over
again with average classes, and continually recast the material
until all obscurities and defects are eliminated. This has been done
thoroughly with the present book, and I have made quite sure that
there is nothing in it which is not easily within the comprehension
of the average student beginning the subject.

The plan of beginning with sulphur, the familiar metals
and their sulphides originated with Ohmann. There can
be no question that this order of topics has many advan-
tages over the usual method of starting with hydrogen and
oxygen. The beginner has yet to acquire the conception
of a gaseous substance. The foundations of the subject
can be laid far more securely when the early part of the
work is concerned entirely with familiar solids.

The oxygen basis has been adopted for the atomic weights. Since
the hydrogen standard is now entirely obsolete, it is no longer
permissible to teach it. Experience has shown that the difficulties
in elementary instruction, which were apprehended at the time the
change to the oxygen standard was made, have not materiaUzed.

A text-book is hardly an original piece of work. I have drawn
freely upon the literature of the science, but there are two authors
to whom I am under special obligations. Otto Ohmann and Alex-
ander Smith. Chemists are to be congratulated upon the fact that
each of these gentlemen has thought it worth while to devote to the
complex problems of elementary chemical instruction the powers of
a penetrating intelligence of the first order.

PREFACE vii

The book covers thoroughly the various requirements and syllabi
which teachers preparing students for college have to consider.

I am indebted to Dr. Harry F. Keller, of the Philadelphia Central
High School, and to Dr. David W. Horn, of the Philadelphia Central
Manual Training High School, for most careful critical readings of
the manuscript and for many valuable suggestions. My thanks
are due to Dr. Keller, also, for lending me the plates from which the
portraits were made. Prof. Shelley and Prof. Morris of the South-
ern High School have assisted me in the reading of the proof.

Most of the illustrations are from original drawings made by my
wife. The remainder have been taken from various sources.

I hardly imagine that the teacher who will give the book a careful
reading will conclude that any part of it is "too difl&cult for the
beginner, " although it is Ukely that no text-book has ever been
written of which this statement has not been made. Let me repeat
that this is a question of fact which is to be decided not bjr o priori
speculation, but by practical class-room work, which, so far as the
present book is concerned, has been carefully done.

Robert H. Bradbury.
Southern High School,
Philadelphia.

CONTENTS

BOOK I— SULPHUR AND ITS COMPOUNDS WITH FAMIL-
IAR METALS.—FAMILIAR ELEMENTS WHICH OCCUR
IN THE FREE STATE IN NATURE

Chapter Page

Introduction 1

I. Sulphur 2

II. Compounds of Sulphur with some Familiar Metals 10

III. Some Native Metals 28

IV. Another Native Non-Metal: Carbon 37

V. The Atmosphere: A Mixture op Non-Metallic

Gases 48

VI. The General Properties of Gases. — ^The Laws of
Boyle and Charles. — The Kinetic Theory of
Matter 61

BOOK II— COMPOUNDS OF OXYGEN

Introduction 77

VII. Oxides of Familiar Metals 78

VIII. Oxides of Non-Metals already Studied: Sulphur
Dioxide, Sulphur Trioxide, Carbon Dioxide,
Carbon Monoxide, Carbon Suboxide .... 93

IX. Water and Hydrogen 112

X. Some Important Oxides Found in Nature: Tin Di-
oxide, Aluminum Oxide, Manganese Dioxide,
Silicon Dioxide. — Thermochemistry 126

XI. The Action op Oxygen upon Sulphides and of Car-
bon ON Oxides. — Metallurgy of Zinc, Lead,
Mercury, Tin and Iron. — Water Gas 140

BOOK III—THE ATOMIC THEORY.— IMPORTANT COM-
POUNDS CONTAINING HYDROGEN

Introduction 153

XII. The Atomic Theory 154

XIIL Compounds op Hydrogen with Sulphur and Nitro-
gen. — Liquefaction of Gases. — Refrigeration 167

X CONTENTS

Chaptbb Page

XIV. Compounds of Carbon and Hydrogen 180

XV. Some Compounds Containing Carbon, Hydrogen

AND Oxygen 191

BOOK IV.— THE SODIUM GROUP OF ELEMENTS.— THE

CHLORINE GROUP
Introduction 205

XVI. Table-Salt: Sodium and Chlorine 206

XVII. Hydrochloric Acid 216

XVIII. Valence. — Determination of Atomic Weights . . 224

XIX. Important Compounds of Chlorine with the Ele-
ments Already Studied 233

XX. Sylvite, Potassium, Caustic Soda and Caustic
Potash. — Sugar Solution Compared with Salt
Solution 241

XXI. Elements which Resemble Chlorine: Iodine, Bro-
mine, Fluorine 258

BOOK V— ACIDS CONTAINING OXYGEN, AND THEIR

SALTS

Introduction 273

XXII. Sulphuric Acid and Its Salts. — Hydrolysis, — The

Electrolysis of Dilute Sulphuric Acid . . 274

XXIII. Nitric Acid and Its Salts. — Compounds of Nitro-

gen and Oxygen. — Chloric Acid and Its Salts . 296

XXIV. The Carbonates: Bleaching Powder, Hydrogen

Peroxide, Ozone 311

XXV. Matches, Phosphorous, Super-Phosphate Fer-
tilizers, Arsenic, Antimony and Bismuth . . 327

XXVI. The Silicates and Borates 337

XXVII. Chromium. — Some Important Rare Elements. —

Radio-Chemistry 342

XXVIII. Some Important Compounds Containing Carbon. —

Colloidal Solution 350

XXIX. The Classification of the Elements. — The Peri-
odic Law 364

XXX. Chemical Calculations 378

APPENDIX 407

INDEX 1 1— 1 22

LIST OF PORTRAITS

Cakl. Wilhelm Scheele Frontispiece

FACING
PAGE

Louis Pasteur 3

Henri Moissan 42

Antoinb Laurent Lavoisier 68

Robert Wilhelm Bunsen 73

J. H. van't Hope 247

Justus von Liebiq 306

Emil Fischer 358

BOOK I

SULPHUR AND ITS COMPOUNDS WITH FAMILIAR

METALS.— FAMILIAR ELEMENTS WHICH OCCUR

IN THE FREE STATE IN NATURE

INTRODUCTION

More than a thousand different materials are found in
the earth's crust. They are called minerals. Most of them
have, by the searching methods of chemistry, been separated
into two or more simpler materials. Lead-glance, the chief
ore of lead, can be separated into lead and sulphur, the
common yellow mineral pyrite into iron and sulphur, and so
on. But a few minerals, like the sulphur, gold and silver of
nature, have resisted all attempts to separate them.

Materials which do not yield to this separating or ana-
lyzing process are called elements. We shall begin our study
of chemistry with the element sulphur, which, in many
respects, forms a suitable ' starting-point. The study of
sulphur will lead naturally to that of some important ores
like lead-glance, copper-glance and silver-glance, each of
which can be separated into two materials, one of which is
sulphur and the other the metal from which the mineral is
named and on which its value as an ore depends. Leaving
sulphur, we shall inquire what other important materials
are foimd as elements in nature, and the concluding chapters
of the first book will be devoted to the atmosphere, which
we shall find to be a mixture of elements.

CHAPTER I

SULPHUR

1. Sulphur Crystals. — Sulphur is often found, near vol-
canoes, as a dull yellow crust upon the rocks. Less often
it occurs in beautiful, transparent, solid masses which have
somewhat the shape shown in Fig. 1. These masses are

bounded by plane surfaces and
are sometimes very perfect in
shape, except where they are at-
tached to the rock. At first sight
it might seem that they had been
given this form artificially, by some
operation similar to that by which
cut-glass objects or gems are shaped.
But they are entirely natural, and the
Fig. 1.— Sulphur crystal as found most perfect Specimens are formed

in nature. Simplest form. ^j^^^^ ^j^^ ^^j^j^^j, particlcS have had

opportunity and time to arrange themselves without being in-
terfered with in any way. They are called crystals of sulphur.
A crystal is a natural solid, boimded by plane surfaces.
Materials which occur as crystals are said to be crystallized
or crystalline. Materials like glass, rubber and glue, which
do not exist in crystalline condition, are said to be amorphous.

2. The Production of Sulphur. — Not very long ago, all the
sulphur of commerce came from Sicily. Large quantities of
it occur there, mixed with limestone, earthy matter and other
impurities. It is extracted by pili' 5 li:mps of sulphur ore
into a heap in a shallow pit lined wich plaster. The heap is
then covered with dust to limit the access of air, and ignited. A
smothered burning follows, during which about half the sulphur
bums away and the rest is melted by the heat and runs out.

One grave objection to this process can be seen at once.
Half the sulphur is wasted. It must not be thought of as de-

^il.

LOUIS PASTEUR
. Frann. 1822. D. 1391

SULPHUR 3

stroyed. No material ever ceases to exist. When it disap-
pears it must go somewhere and it is usually an easy task to
find out what has become of it. In this case the product
of the burning of the sulphur passes into the air, where it causes
great injury to all forms of plant life, and this is another
very bad feature of this method of producing sulphur.

Vast quantities of sulphur were formerly employed in
making "oil of vitriol" (sulphuric acid), which is the most
important of all chemical products, and is made by the mil-
lion tons every year (two million in the United States alone).
For reasons that we shall understand later, sulphur is no
longer employed as the raw material of this great industry.

The United States, which was an important market for
the Sicilian product, has begim to produce enough sulphur
not only to supply its own needs, but also to export consider-
able quantities. Workable deposits occur in Nevada,
Wyoming and Utah, but, so far, Louisiana has been the
chief producer. The method of extraction used in the
United States is as follows: Four concentric iron tubes are
driven into the sulphur bed. The inner tube is one inch in
diameter, the next three, the next six, and the outer tube ten.
Through the three-inch tube, water, heated under pressure
to a temperature much above the boiling-point, is forced
into the deposit to melt the sulphur. Compressed air is
driven into the one-inch tube. Melted sulphur, mixed with
air, then bubbles up through the outer tubes. The melted
sulphur is allowed to run into huge bins, fifty feet high, built
of planks, where it solidifies to form a block of practically pure
sulphur, which may contain 100,000 tons. This is broken
up by blasting, and shipped.

3. Uses of Sulphur.— Sulphur has some important wses.
Grapevines and fruit trees are subject to the attack of
parasites which have devastated orchards and vineyards
and led to losses of millions of dollars. Pasteur found that
finely powdered sulphur, and preparations made from it, are
an effective means of destroying these pests. Another use

AN INDUCTIVE CHEMISTRY

is for the bleaching of wool, which is done by hanging the yam
or cloth in a chamber in which sulphur (tV of the weight of
the wool) is burned. Silk is often bleached in the same way.
Rubber is always "vulcanized'' before it is fit
for any practical purpose. This is a process in
which it is made to take up sulphur, 2 or 3 per
cent for the soft varieties, and for hard rubber
considerably more.

4* Properties of Sulphur. — ^There are several
different varieties of sulphur. The form whose
crystals are found in nature is called a-sulphur
(a is the first letter of the Greek alphabet). The
roll-sulphur of the laboratory is simply a mass
of crystals of or-sulphur.

There is another kind of sulphur which can be

Fia.2.— Crys- made by melting a-sulphur and letting it freeze.

by the frees- We shall Call this material /5-sulphur (/? is the

ing of melt- gecoud letter of the Greek alphabet). The shape

of the crystals of /^-sulphur is shown in Fig. 2.
Since )5-sulphur changes back to or-sulphur on being pre-
served, its properties must be determined with a sample
freshly prepared.

c:^^.

Properties ^ op ^-Sulphur and )8-Sulphur ^

CUSULPHUR

)8-SXJLPHUR

Shape of Crystals

See Fig. 1.

See Mg. 2.

Specific Gravity

2.06

1.96

Melting Temperature

114.5^

119^

Tenacity

Very brittle

Distinctly flexible

Color

Lemon-yellow

Pale honey-yellow

Behavior when pre-

Does not change

Changes to o-sul-

served at ordinary

phur

temperatures

Behavior when kept

Changes to jS-sul-

Does not change

at 100**

phur

^ The color, odor, crystalline form of a material, its behavior when
heated and acted upon by other substances, etc., are called its properties.
2 All temperatures given in this book are Centigrade.

SULPHUR 5

5. Meaning of the Term " Substance." — ^The two kinds of
sulphur just discussed are quite diflferent and yet they are
ahke in the fact that they contain sulphur and nothing else.
A heap of powdered sulphur presents a diflferent appearance
and is suited to diflferent purposes from the same material
in a compact roll, and yet, to the chemist, the two are identi-
cal. He expresses this by saying that sulphur is a substance
which can exist in various conditions. Laboratory experi-
ence with sulphur will show the student that it may take
the form of a liquid, a vapor and at least two diflferent solids.
There ai^, in fact, four or five other soUd crystalline modi-
fications which have been studied but which we have no
time to consider. Then there is the soft sulphur made in
the laboratory, which the student will probably regard as
partaking of the nature of both solid and liquid. In just the
same way, water is a substance which can take the form of
ice (solid), water (liquid), and steam (vapor) under diflferent
conditions.

6. Substances are Homogeneous. — It is possible that
in the Physical Geography class the student has examined
granite. A glance is enough to show that there are three
things in it and he probably knows that these are the three
minerals quartz, felspar and mica. Granite is not a sub-
stance, for it is not homogeneous. This means simply that
diflferent parts of it are diflferent. The point of a needle can
be placed in succession upon three diflferent substances in a
block of granite. It is, then, a mixture of these three sub-
stances. But no diflferent substances can be indicated in
a roll of sulphur. It is homogeneous. Chemistry deals
chiefly with homogeneous materials, like sulphur and water.

7. More about ttie>Forms of Sulphur. — If the student pre-
served some of the /5-sulphur, which he made by melting
roll-sulphur, he must have noticed that each of the needle-
like prisms became opaque and brittle, and, at the same
time, took on a lemon-yellow color. No doubt this made him
suspect that the /5-sulpbur did not "keep''; that it turned

6 AN INDUCTIVE CHEMISTRY

back again to or-sulphur, and, in fact, that is exactly what
happened. We have a short way of indicating changes of
this kind, thus:

/^-sulphur — >■ a-sulphur (i)

The arrow may be read "changes to," "produces" or "yields."
Exactly the same thing occurs if a little soft sulphur is laid
aside. The transparent, elastic threads become opaque,
brittle and yellow:

Soft sulphur '■ — >- a-sulphur. (2) •

In this case the change is very slow, and it may be years
before it is complete.

The only form which "keeps" is a-sulphur. The other
forms all change into or-sulphur when they are preserved
at ordinary temperatures. Our science expresses this be-
havior by the statement that or-sulphur is the stable form,
or the natural state of sulphur. This explains the fact that
£v-sulphur is the only form foimd in nature. The others
may have been formed, but they could only exist for a short
time.

A crystal of or-sulphur will remain for any length of time
in the cold, without change of any kind. The sulphur of
nature, some of which was produced long before the dawn
of history, is a striking proof of this. But a-sulphur, on
the other hand, becomes unstable when heated gently.
Put a crystal of it in a dry test tube, cork the tube, and sur-
round it with boiling water, and the crystal slowly becomes
opaque. Examination with the microscope shows that it
has changed to a mass of little prisms of /^-sulphur:

flf-sulphur — >■ /^-sulphur (3)

Expressions of the sort given above are called equations.
Equation (3) is evidently the exact reverse of (i), above.
But there is no contradiction, if we remember that (i) takes

SULPHUR 7

place only in the cold and (3) only when the sulphur is
heated. We can combine the two in one expression:

/^sulphur < ^' o'-sulphur (4),

but we must remember to read from left to right if we are
thinking t^bout the behavior at ordinary temperatiu*es (i),
and from right to left if we mean the behavior at 100® (3).
We can describe the boiling and freezing of water by simi-
lar equations. For the boiling we write:

Liquid water < ^ steam.

We read from left to right for temperatures above the boil-
ing-point (100**), and from right to left for temperatiu*es
below the boiling-point. In the same way we can write
the freezing of water:

Ice < ^ Liquid water,

and, recalling the fact that water freezes at 0®, we read from
left to right for temperatures above 0® and from right to
left for temperatures below.

Related Topics

8. The Melting of Ciystalline Substances. — If sulphur is
heated and stirred with a thermometer it is found that the instru-
ment registers 114.5** when the sulphur begins to melt and
remains at that temperature until the solid is all melted. The
abruptness of this change should be noted. It takes place sharp-
ly at 114.5°, not over a considerable number of degrees as might
be expected, and each portion, as it melts, changes at once from
a bright yellow, rigid solid to a thin amber liquid, without pass-
ing through any pasty or half liquid condition.

In the change of one gram of sohd sulphur to liquid sulphur
a considerable quantity of heat is absorbed. This quantity
can easily be measured. It is called the heat of fusion of
sulphur.

An abrupt passage from sohd to liquid at a definite tempera-
ture always occurs when a crystalline substance melts. Ice be-
haves in the same way, except that the temperature of melting is

8 AN INDUCTIVE CHEMISTRY

0**. If, in a very cold room (below 0**), we were to fill a test tube
with cracked ice, put a thermometer in the ice and heat the tube
with a flame, the ice would all remain solid until the temperature
was 0** and the thermometer would remain at zero until the
ice had all melted. Each second a little of the ice would change
from ice (with all the properties of a solid) to water (with the
very different properties of a liquid), and there would be no
sign of any pasty condition between.

One gram of ice absorbs, in melting, enough heat to warm
80 grams of water through 1® C. This large heat of fusion
plays an important part in regulating climate, tending, as it
does, to prevent rapid changes of temperature.

9. The Melting of Amorphous Materials. — Very different is
the melting of amorphous substances. Glass is the best material
to experiment with. Hold a rod in the flame. Before it is red-
hot it bends and sags, showing that it has begun to melt. The
hotter it becomes the more it partakes of the nature of a liquid.
It is easy to get it sufficiently liquid to pull out into long threads,
but impossible, with the Bunsen flame, to push the heat to the
point where the glass becomes a thin liquid.

Glass has no melting-point. From the point where it begins to
soften, to the point where it is a liquid as thin as melted sulphur,
there is a range of 1000° or more, and in this range there is no
particular temperature which can be picked out as the melting-
point. It acts, in fact, as though it was at all times a liquid
(even in the cold, although then a very stiff one), and simply be-
comes thinner and thinner the more it is heated. The quantity
of heat which is absorbed during the melting of one gram of glass
is so small that it has never been measured.

Other amorphous substances, like glue and rubber, behave in
the same way. They melt over a range of temperature, and
the quantities of heat absorbed in the melting are too small
to measure. Crystals are the only real solids, and substances
like glass, glue and soft sulphur are simply liquids which have
become very stiff {viscous is the scientific word) by cooling, with-
out ever really becoming solid at all.

10. The Abruptness of Chemical Changes. — When crystals
melt, then, they pass, at a definite temperature, from a com-
pletely solid state to a completely liquid state, with no inter-

SULPHUR 9

mediate pasty condition to fill the gap. Now all of the changes
in matter which form the subject of chemistry are of this sin-
gularly abrupt nature. Clean a piece of iron (for instance, a
nail) with sandpaper until it is bright, and expose it to the
weather for a while. When examined it will be found that it
bas begun to turn to rust, which is red-brown and much less
tenacious than iron — easily rubbed to a powder with the hand.
There are only two things present; rust, and iron which has
not yet had time to turn to rust. We look in vain with a lens,
or even a microscope, for any intermediate substance.

Definitioiis

Crystal. A natural solid, bounded by planes.

Crystalline. Composed of crystals.

Amorphous. Not crystalline.

Homogeneous. Composed of the same material and having the
same structure throughout; uniform.

Substance. Any particular homogeneous material; for instance,
sulphur, water, sugar or salt.

Mineral. A substance found in the earth's crust.

Ore. A mineral from which some important product, usually a
metal, is obtained.

Deposit, A considerable mass of ore or useful mineral.

Viscoiis, Thick; stiff; sticky; imperfectly liquid.

CHAPTER II

CX)MPOUNDS OF SULPHUR WITH SOME FAMILIAR

METALS

II. Lead-glance, or Galenite. — In many localities in the
United States, especially in Missouri, Idaho, Colorado and
Utah, occur large quantities of a mineral called lead-glance by
the miners, and galenite by the mineralogists. Its crystals

take the form of cubes (Fig. 3), less fre-
quently of octahedrons (Fig. 4), and
very often of a combination of both
(Fig. 5). Its appearance recalls that
of lead, for it has
a blue-gray color
and a metallic lus-
ter, but, although
dense (specific
gravity 7.6) it is not as dense as lead
(specific gravity 11.2). Under the
hammer, lead flattens out, but lead-
glance is very brittle and breaks always

along three

Fig. 3. — Cube.

rf^r\

planes at right Fig. 4.— Octahedron.

angles to each

other, so that the broken mass con-
sists of cubes.

Lead is readily obtained from galen-
ite. When the mineral is heated on
charcoal, with the flame of the blow-
pipe, a globule of lead is left. At
the same time, the sharp odor of burning sulphur is
perceived. When the powdered mineral is heated with
nitric acid, sulphur is formed, and can be identified
by its color and by drying and burning it. Nitric acid

W^---7Ar ^

FiQ. 5. — Cubo-octahedron.

SULPHUR WITH SOME FAMILIAR METALS 11

contains no sulphur, so the latter must come from the
galenite.

It seems, then, that it is easy to obtain lead from galenite.
Galenite is almost the sole source of the lead of commerce.
Sulphur, also, can readily be obtained from it. But, from the
pure mineral, nothing but lead and sulphur can be obtained.

The next question that arises is whether galenite can be
produced by putting together lead and sulphur. Lead and
sulphur are mixed in a test tube and heated. The resulting
mass has the properties of lead-glance. There are no large
crystals, for the product is formed too quickly, but cubes can
be obtained by heating gently for a long time. On char-
coal and with nitric acid the artificial product behaves
like the galenite of nature. Our conclusion, then, that
galenite is composed of lead and sulphur, is based not only
on the analysis (or taking apart) of the mineral into these
two substances, but also on the synthesis (or putting together)
of lead and sulphur to make it.

12. The Metal from Lead-glance. — Lead, the metal
which we have obtained from galenite, is softer than gold
and not as dense. When freshly cut, it has a bright blue-
gray metallic luster, but this is rapidly dimmed by rusting,
giving place to the familiar dull gray color of the metal.
However, the film of lead rust formed protects the mass
beneath and the metal is quite permanent in the air.
No doubt the student has noticed that melted lead rusts
more rapidly. It becomes covered with a yellow scum
called litharge, which has no metallic luster and does not
resemble lead in the least. By heating long enough all the
lead can be converted into this material, which always
weighs more than the lead from which it is made. 100 parts by
weight of pure lead will always yield 107.7 parts of litharge.

In the same way, when lead and sulphur are heated to-
gether to form artificial lead-glance, 100 parts of lead by
weight will always form 115.5 parts of lead-glance, taking
up 15.5 parts of sulphur. If we use more lead than corre-

12 AN INDUCTIVE CHEMISTRY

spends to these proportions, the excess of lead remains in
the tube, mixed with the lead-glance. On the other hand,
if we take too much sulphur, the excess of sulphur is driven
off by the heat and escapes in the yellowish smoke which
issues from the tube.

13. Practical Aspects of Lead. —About a million tons of
lead are made in the world each year, of which the United
States furnishes about 350,000 tons. Spain and Germany
are also important producers.

The metal is plastic when warm and is formed into pipes
which are largely used for covering electric cables and in
plumbing. Shot is made of lead containing a little arsenic.
Solder contains lead and tin. Type-metal contains lead,
tin and antimony. Lead resists the action of acids and
other chemicals better than the other cheap metals and,
for that reason, is • largely used in practical chemistry.
The great chambers in which sulphuric acid is manufactured
are made of lead. "White lead" and "red lead" are no
doubt familiar to the student from their extensive use as
paints. We shall see that they contain lead, and large
quantities of the metal are used in making them. Lead and
substances containing it are poisonous. Workmen who deal

with them are subject to chronic lead
poisoning which usually destroys
the health in a short time.

14. Pyrite or "FooPs Gold."—
The very common and important
mineral, pyritey is yellow, but the
color is much lighter than that of
gold. It is more like the color of
pale brass. Its specific gravity (5)

Fig. 6.-^te^ry8taI. '» ^^'y ^bout OUC-foUrth that of

gold (19). It is readily distinguished
from gold by its hardness. It is too hard to be scratched by a
knife. Gold is very soft. Like lead-glance, pyrite often crystal-
lizes in cubes or in octahedrons. Another frequent form is

SULPHUR WITH SOME FAMILIAR METALS 13

shown in Fig. 6. Pyrite occurs abundantly in many localities.
The Rio Tinto mines in Spain have yielded great quantities of
it. In the United States it is mined chiefly in Virginia. Most
of it goes into the sulphuric acid manufacture. The greater
part of the sulphuric acid of commerce is now made from
pyrite.

15. Composition of Pyrite. — Now, sulphuric acid, as the
name indicates, is a substance containing sulphur, and from
the use to which pyrite is put we might suspect that it was
rich in sulphur. When the mineral is heated in a glass
tube, closed at one end, a yellow ring of sulphur forms
in the upper part of the tube. The heated mineral has lost
the brass-yellow color of pyrite and has become magnetic.
This suggests the presence of iron. When some of the pow-
dered mineral is treated with nitric acid, the sulphur is left,
just as with lead-glance. Further evidence can be obtained
by heatmg the mmeral on charcoal with the blowpipe.
The pyrite bums with a blue flame and the sharp odor of
burning sulphur is noticed. The substance left on the
charcoal betrays the presence of iron by being attracted by
a magnet.

16. Iron, the Metal of Pyrite. — IroUj the metal contained
in pyrite, is white and lustrous when pure and will take a
high polish. The commercial forms of iron contain various
impurities which have a marked effect upon its strength.
The study of the effect of impurities upon iron is a large and
important subject. For instance, commercial iron always
xjontains a little sulphur, but if the quantity of sulphur is
greater than a few hundredths of one per cent, the iron is so
weak as to be worthless.

To mention the uses of iron would be to write an account
of modem civilization. About sixty million tons of it are
made each year, of which the United States yields nearly
one-half. Germany and England are the other great pro-
ducers. About five-sixths of this enormous quantity is con-
verted into steeL

14 AN INDUCTIVE CHEMISTRY

17. Copper Pyrite (Chalcopyrite). — ^Along with pyrite,
often in the same specimen, is found a mineral called chalco-
pyritej somewhat like pyrite in appearance, but of a deep

gold-yellow color. It is much softer
than pyrite, and can be easily scratched
with a knife. The shape of the crystals
(Fig. 7) is quite unlike that of the
pyrite crystals.

Heated in a tube sealed at one end,
chalcopyrite behaves like pyrite, yield-
FiG. 7.--A crystal of chai- j^g ^ ring of sulphuF. On charcoal,

with the blowpipe flame, it yields a
magnetic globule and the odor of burning sulphur. It is
clear that sulphur and iron must be contained in it.

When the powdered mineral is treated with nitric acid, it
leaves a residue of sulphur, but the liquid over the sulphur
is blice, which is not the case when pyrite is treated in the
same way. If this blue liquid is carefully heated until most
of the nitric acid has been driven off and then some water and
an iron nail are added, the iron rapidly becomes coated with
a red metal which is recognized as copper. The copper did
not come from the nitric acid, for nitric acid contains
no copper. It could not come from the nail. So here is a
third material obtained from the chalcopyrite. Lead-glance
and pyrite can be separated into only two substances, but
chalcopyrite yields three,

Chalcopyrite is an abundant and important copper ore. It
occurs at many places in the eastern United States, for
instance, near Phoenixville, Pa., and at Ellenville, N. Y.,
but is most abundant in the West, notably in Montana.

18. Copper. — Copper is rose pink. It can be obtained in
leaves so thin as to transmit a green light. It melts much
more easily than iron. Pure iron melts only at 1600°, which
is far beyond a white heat (1500°). Copper melts at 1100°,
which is a yellow heat. Except silver, copper is the best
conductor of electricity (and of heat) among the metals.

SULPHUR WITH SOME FAMILIAR METALS 15

The metals as a class conduct both heat and electricity very
much better than non-metallic materials. Copper is ex-
tensively used for wires and cables for conducting the electric
current. It must be purified with care, since small amounts
of impurities greatly reduce the conducting power. Copper
ntst is green. It is formed more slowly than iron rust, and,
like many substances containing copper, is poisonous.

All the iron of the world is obtained from iron ores, that
is, substances containing iron. The metal itself scarcely
occurs in nature and is nowhere found in sufiicient quantities
to mine. Most of the copper is obtained from copper ores,
like chalcopyrite, but copper metal, unlike iron and lead,
is found abundantly in some localities. In the copper
mines on the shore of Lake Superior, in northern Michigan,
masses of the metal weighing himdreds of tons have been
found. About 850,000 tons of copper are produced in
the world each year, of which the United States furnishes one
half. The chief copper-producing states are Montana,
Arizona, Michigan and Utah.

The method employed in extracting the copper from
chalcopyrite, or some similar method, would show the pres-
ence of very small quantities of copper in many materials
of the mineral world, and in some animal and plant struc-
tures. Thus, traces of it are contained in the red feathers
of some birds, in hops, in the human kidneys and in the
blood of the cuttlefish, which is blue when arterial, and color-
less when venous.

19. Cinnabar. — The mineral cinnabar is mined exten-
sively at New Almaden, Cal., at Almaden in Spain and at
Idria in southeastern Austria. It is easily distinguished
from most other minerals by its red color, its softness, and
its high specific gravity (8). Heated on charcoal, it dis-
appears in a gray smoke, giving at the same time the odor
of burning sulphur. Heated with a little iron powder, in
a test tube, a ring forms in the cooler part of the tube which
is seen to consist of small drops of mercury (quicksilver).

16 AN INDUCTIVE CHEMISTRY

It appears, then, that cinnabar contains mercury and sul-
phur. Synthesis confirms this and makes it unnecessary to
search for other constituents. For when sulphur is melted
and heated with a little mercury, a substance having all the
properties of cinnabar is formed.

20. Mercury. — Mercury is obtained by heating cinnabar
in a current of air. The gases are passed through long flues
in which the mercury deposits.

Mercury is the only liquid metal. It has a bright white
metallic luster and a high specific gravity (13.6). At 357°
it boils, passing into a colorless vapor. This vapor is formed
slowly in the cold. Mercury, left standing in open vessels,
shows a loss in weight which can easily be measured on a
good balance. If a piece of gold leaf is suspended from the
stopper of a bottle containing mercury, the gold will be
slowly whitened by mercury deposited upon it.

Mercury freezes at about -40° to a mass which resembles
lead, but is lighter in color. Solid mercury can be beaten
out, but the part of the hammer which strikes it must be
covered with a leather pad, or the mercury must be wrapped
in a cloth, for contact with the steel of the hammer (which
of course has the ordinary temperature of the room) will im-
mediately melt it.

Mercury is used, on account of its high specific gravity,
for filling barometers. When heated its expansion is very
regular, and this makes it an excellent liquid for thermom-
eters. The zinc employed in batteries is rubbed with mer-
cury to prevent it from being acted upon when the battery
is not in use. Mercury and substances containing it are
poisonous. Many materials made from it are used in medi-
cines. The annual production of mercury of the world is
about 3000 tons.

21. Sphalerite, or Zinc Blende. — Zinc blende occurs abun-
dantly with the lead-glance of Missouri, Wisconsin, Iowa
and Illinois. This has caused it to be mistaken for galenite,
but zinc blende has a much lower specific gravity. The

SULPHUR WITH SOME FAMILIAR METALS 17

crystals have a different shape (Fig. 8) and a very different
luster. Instead of the marked metallic appearance of lead-
glance, zinc blende is usually semi-transparent, and has the
luster of a piece of rosin, the resinous luster.

Treated with nitric acid, zinc blende leaves a residue of
sulphur. On charcoal before the blowpipe the odor of burn-
ing sulphur is noticed. No metallic globule
is obtained, but a coating forms on the char-
coal which is yellow when hot and white when
cold. This is composed of a substance with
which the student is probably familiar. It is
"zinc white," so called because it contains
zinc and it is extensively used as a white
paint. There is no good way of getting the
zmc out of zinc blende in the laboratory, ^^ ^ wendT**
but on a large scale this is easily done
and zinc blende is the main source of the zinc of commerce.

When a small quantity of zinc dust is mixed thoroughly on
an asbestos plate with about half its weight of finely powdered
sulphur, and a flame applied, the mixture bums like gunpow-
der. A white mass, which is the same substance as zinc blende,
is produced. Its appearance is quite different from that of
the mineral zinc blende, because it is formed so quickly.

22. Zinc. — Zinc has not been found as metal in nature.
It is blue-white, crystalline and, when cold, brittle. At
about 130® it becomes malleable and sheet zinc is made by
rolUng the metal with heated rollers. The sheets retain
their flexibility when cold. At a somewhat higher tempera-
ture zinc again becomes brittle, and can be powdered in a
mortar. It melts at 419° which is below a visible red heat
(500°). Somewhat above its melting-point, it takes fire —
if the air has access to it — and bums to a loose white powder
of zinc white, which weighs more than the zinc from which it
is obtained. Zinc boils at a bright red heat (930°).

Lead, iron, copper and mercury were known and used by the ancients,
but zinc came to Europe from eastern Asia as a curiosity during the

18 AN INDUCTIVE CHEMISTRY

16th century, and has only been important commercially for about
a hundred years. The reason can be deduced from laboratory
experience. Zinc is more difficult to separate from its ores than the
other metals just mentioned. The ancients had no knowledge of chem-
ical science. They only knew the metals which occurred in the free
state in nature, like silver and gold, and those which could be very
easily obtained from their ores, like lead.

Sheet zinc is used for roofs, gutters and other construction
where lightness is important (specific gravity, 7), but its
chief use is in ''galvanizing" iron. The iron is cleaned and
dipped in melted zinc. The object is to protect the iron
from rust. The zinc coating serves this purpose better than
any other covering. The process is applied to telegraph
wires, fencing, sheet iron for building construction, and, in
fact, to all iron which is to be exposed to the weather. Even
if a small hole forms in the zinc, laying bare the iron, the
latter will not rust. The zinc must rust first, when iron and
zinc are in contact. When iron is plated with tin, the re-
verse is true. The moment a hole lays bare the iron, the
iron begins to rust and the rusting is stimulated by the
presence of the tin, which itself stops rusting, being pro-
tected by the iron. This is the reason that a roof of tin
plate requires frequent painting, while galvanized iron lasts
very well without paint.

Upwards of 800,000 tons of zinc are made each year,
mostly from zinc blende. The United States and Germany
are the chief producers, each yielding about one-third of the
world's total.

23. Mixture and Compound. — Let us mix 20 grams of
copper filings with 10 grams of finely powdered roll sulphur.
We should expect the resulting material to consist of little
fragments of copper and of sulphur. That this is really its
structure can be seen with a lens or a microscope. The two
substances are just as truly separate as when they were in two
different bottles. The mixing has merely brought them
closer together. The mixture is not homogeneous, like sul-
phur and the sulphur-containing minerals we have just

SULPHUR WITH SOME FAMILIAR METALS 19

studied. It is like a piece of granite in the respect that
certain parts of it differ from other parts in properties.

We can easily prove by experiment that the colorless
liquid, carbon disulphide, takes up sulphur easily and de-
posits it again when the liquid dries up. But carbon disul-
phide has no effect upon copper, as can be shown by shaking
up a little of it with some copper filings in a test tube.

24. Separating Mixtures. — ^We can now predict the action
of carbon disulphide upon the mixture we have made. When
some of it is sliaken up with carbon disulphide in a test tube
and the liquid poured off into a dish, copper remains in the
test tube. When the liquid in the dish has evaporated a
deposit of sulphur crystals is left. In exactly the same way
one might separate a mixture of salt and sand by treating
it with water. The salt would dissolve and the sand remain.

Another method of separating the mixture of copper and
sulphur can be based upon the fact that sulphur (specific
gravity, 2) is far lighter than copper (specific gravity, nearly
9). Make a liquid whose specific gravity is greater than 2
and less than 9. Throw some of the mixture into it. The
copper sinks and the sulphur floats. This method is largely
used by geologists in separating powders consisting of min-
erals of different specific gravity.

Or, stir up some of the mixture with water. The sulphur
remains suspended in the water much longer than the cop-
per, and by pouring off at the right time, a partial separation
can be carried out. This method does not work well on a
small scale, but is extensively employed for separating various
mixtures in practical work, where large quantities are dealt
with. We should carefully note the principle of it.

One fact about the mixture is self-evident, and of great
importance. We can make it in any proportions we choose.
We took 20 parts of copper to 10 of sulphur so that the mix-
ture contained:

Copper 66.67%
Sulphur 33.33 %

20 AN INDUCTIVE CHEMISTRY

but we might as well have taken some other proportion, so
far as the making of the mixture was concerned. The com-
position of a mixture is under the control of the person
who makes it.

25. Copper-glance. — Now let us lay aside the mixture for
a moment and, as a contrast, examine a homogeneous sub-
stance composed of copper and sulphur. Copper-glance is
found at Bristol, Conn., at Butte, Mont., and at many
other places, e. g, in Siberia and South America. It is
black-gray and has a metallic luster. It can be proved to
consist of sulphur and copper by the same methods employed
in analyzing the other sulphur minerals. But no copper or
sulphur can be seen in it. The most powerful microscope
shows merely a black-gray, uniform mass.

When copper-glance is powdered and shaken up with
carbon disulphide, the powder is unaffected. No sulphur
is taken up by the liquid, for, if it is poured off and allowed
to evaporate, nothing remains.

When the powder is thrown into a liquid whose specific
gravity is higher than that of sulphur, it will all sink; no
sulphur appears on the surface. A liquid whose specific
gravity was higher than 5.5 (the specific gravity of copper-
glance) would make all of the powder float, but there are
difficulties in the way of obtaining a suitable liquid.

Nor can any separation of the copper and sulphur be car-
ried out by stirring up the powder with water and pouring it
off when partial settling has occurred. Both the portion
which settles and that which remains suspended consist of
copper-glance. The only difference h that the latter is
somewhat more finely powdered than the former.

Whether they come from Connecticut or Montana, from
South America or Siberia, the pure crystals of copper-glance
always contain the same proportions of copper and
sulphur-

Copper 79.87%
Sulphur 20.13 %

SULPHUR WITH SOME FAMILIAR METALS 21

This is a fundamental distinction between copper-glance
and our mixture, which could have any composition we saw
fit to give it.

26. Synthesis of Copper-glance. — It is easy to transform
our mixture of copper and sulphur into artificial copper-
glance. Place it in a dry test tube and apply heat to one
point. A glow begins here and spreads through the mass.
Clearly a change is occurring which gives out much heat.
When the action is over, we find in the tube a gray-black
mass which is similar to copper-glance in appearance, but
without well formed crystals because it has been formed so
quickly. The copper and sulphur can be obtained from it
again, in the same way as from the mineral. Like the copper-
glance, it resists the methods of separation based upon the
use of carbon disulphide or upon the difference of specific
gravity of copper and sulphur.

It will be seen that there is a profound difference between
the state of the copper and the sulphur in the mixture, and
the condition of the same two substances in copper-glance.
Our science expresses this difference by the statement that
copper-glance is a compound of copper and sulphur. The
other minerals which were analyzed into their constituents,
and synthesized from their constituents, were also compounds
of sulphur with the different metals, lead, iron, copper,
mercury and zinc. Using our experience with them as a
basis, we can state the distinction between compounds and
mixtures as in the table on the following page.

27. Discussion of the Table. — ^The five statements in

column B are true of all compounds without exception. The

first four statements in colimin A apply only to mixtures of

powders like the mixture of copper and sulphur or of zinc

dust and sulphur. There is a great and important class of

mixtures called solutions, of which these four statements are

not true at all. We shall study them in detail later, but, at

present, we need only stir up a spoonful of sugar in a cup of

water to have a mixture to which these four distinctions in
3

AN INDUCTIVE CHEMISTRY

Distinctions between Mixtures and Compounds

A — Mixtures

B — Compounds

I Appearance

Not homogeneous

Homogeneous

2 Separation

Easy by methods

Impossible by meth-

based upon the dif-

ods based upon the

ferent physical

physical properties

properties of the

of the constituents

constituents

3 Properties

Can be calculated

Have no relation to

from those of the

those of the con-

constituents

stituents

4 Heat-production

None

Usually much heat

during formation

given out. Some-
times heat ab-
sorbed

5 Proportions of the

Can be varied at will

Always the same in

constituents

the same com-
pound

column A do not apply. For (l) the liquid is homogeneous,
(2) it can not be separated into sugar and water by methods
similar to those we employed with the mixture of copper and
sulphur, (3) the properties of the sugar are entirely lost/
(4) there is a decided disappearance of heat when the water
takes up the sugar. Distinction (5) holds good, however, in
this as in all similar cases, for we can dissolve little or much
sugar in the water up to a certain limit. Therefore, the
constancy of composition of compounds is the great distinction
between them and mixtures. This fact, that the composition

* Very likely the student will object that the taste of the sugar re-
mains in the liquid. But there is no such thing as the taste of solid
sugar. For it must always dissolve in the saliva before it is tasted
and the taste is that of the solution.

SULPHUR WITH SOME FAMILIAR METALS 23

of the same compound is always the same, is called the law
of definite proportions.

28. Chemical Change. — The compomids of sulphur with
other substances are called sulphides. Lead-glance is lead
sulphide; copper-glance is copper sulphide; cinnabar is
mercury sulphide. When copper and sulphur are heated
together they unite to form a new substance, copper sul-
phide. Notice the abruptness of the change. As each
portion of the mixture in turn changes to the compound,
copper sulphide, the properties of copper and sulphur vanish
and the properties of copper sulphide appear. There is no
gradual passage from mixture to compound, no intermediate
stages can be discovered.

When all the properties alter at once in this abrupt way
we call the process a chemical change. The experiments
in which we made the compounds of sulphur with lead,
mercury and zinc were chemical changes.
So, also, is the burning of zinc in the air
to form zinc white.

29. The Business of Chemistry. — ^The
task of Chemistry is the study of chemical
changes. We have proved that copper
and sulphur combine to form copper
sulphide. The next step is to ascertain
what quantities of the two substances
unite. Weigh a little fine copper wire m p,^ ^ _^ ^^^^^
a porcelain crucible (Fig. 9) and add cnidbie.
about an equal weight of sulphur. Heat

the covered crucible to redness and weigh again. The
substance in the crucible is now copper sulphide and the
gain is the sulphur which has combined with the copper.
In this way we could show that about 80 parts of copper
combine with about 20 parts of sulphur to form 100 parts
of copper sulphide, all by weight.

30. Effect of Heating on the Speed of Chemical Changes.
—We had to heat the copper and sulphur to make them com-

24 AN INDUCTIVE CHEMISTRY

bine. This fact gives rise to many questions. For instance,
does the change occur at all in the cold or not? Does it
begin to occur at some definite temperature, say a red heat?
Or does the miion go on slowly in the cold, so slowly that
we cannot wait for it and therefore apply heat in order to
quicken it?

We can easily show that sulphur combines with silver in
the cold. Place a bit of sulphur in the bowl of a silver spoon
and look at it every day or two. A black stain of silver
sulphide appears on the sp)oon, siurounding the sulphur for
some distance on all sides. This also proves that sulphur,
like mercury, passes into vapor slowly in the cold, for other-
wise only the part of the spoon in contact with the lump
would be blackened. In a similar way, it could be shown
that sulphur acts upon copper slowly in the cold and that
the only effect of heating is to quicken the change.

31. The Elements. — In the laboratory, we have separated
lead-glance into sulphur and lead, cinnabar into sulphur and
mercury, zinc blende into sulphur and zinc, pyrite into iron
and sulphur and chalcopyrite into iron, copper and sulphur.
No one has ever succeeded in sphtting up sulphur, lead,
mercury, zinc, iron or copper into simpler substances. Just
as we have worked with these minerals, so chemists have
worked with the other compoimds found in the crust of the
earth, with the object of separating them into simpler mate-
rials. As a result, they have obtained about eighty sub-
stances, which resist further separation.

A possible explanation of the failure to split up the ele-
ments is that they are in reality simple substances. For
instance, it is quite possible that sulphur has never been
separated because there is really nothing but sulphur in it
and there are no simpler materials into which it might be
separated. This, however, is a possibility merely, and the
history of our science warns us to be careful how we make
statements that any task will always remain beyond its
power. Water and air were regarded for centuries as ele-

SULPHUR WITH SOME FAMILIAR METALS 25

ments, but the development of chemical methods has shown
that the first is a compound and the second a complex
mixture.

"Chemistry advances toward its goal by dividing, subdividing, and
again subdividing, and we cannot tell what will be the limit of its
victories. We cannot be sure that the substances which we call simple
at present are indeed simple; all we can say is that they are the limits
to which chemical analjrsis has arrived, and that, with our present
methods, we are unable to subdivide further." (Lavoisier, 1789.)

32. An element is a substance which has not yet been
(and perhaps may never be) separated into simpler sub-
stances. Or, an element is a substance of which the following
statement holds good: When it is completely converted into
another substance, the product will weigh more than (or,
in rare cases, the same as) the substance before the chemical
change. Examples: lead can be converted into lead sul-
phide, which weighs more than the lead, ar-sulphur can be
converted into /8-sulphur whose weight is the same as that
of the ar-sulphur. Lead cannot be completely converted into
a product which weighs less than the lead.

A compound is a homogeneous form of matter which can
be separated into at least two substances, and always yields ^
them in the same proportions by weight.

A solution is a homogeneous form of matter which may
contain its constituents in any proportions by weight, up
to a certain limit. Example: brine, which may contain
little or much salt up to the point where the water refuses
to take up any more.

A mechanical mixture is non-homogeneous matter. It is
composed of at least two substances, lying side by side, and
may contain these substances in any proportions whatever.

The law of definite proportions: The composition of the
same compound is always the same. The experiments made
to test this law would have detected a variation of less than
one part in a million. They have failed to show that there
is any variation at all.

26 AN INDUCTIVE CHEMISTRY

In a chemical change all the properties of a substance
change at the same time, abruptly. No gradual transition
can be traced. We usually express this by saying that a
new substance is produced. Hang weights an ounce at a
time on a spring balance (scale used for weighing ice, for
instance). The spring is pulled out in a perfectly continu-
ous way. Two oimces pull it out twice as much as one; the
elongation is proportional to the weight applied. None of
the other properties of the spring are altered. This is a
physical change* Innumerable changes of this sort occur
and their study is the province of the science of Physics,
The rusting of iron is a chemical change (p. 9).

Chemistry is the science whose business it is to study
chemical changes. This study includes not only the exam-
ination of the products, but also that of the change itself
and the study of the influence of pressure and temperature
upon it. The name of our science is derived from the
ancient Egyptian word Ch6mi, which was the name the
Egyptians gave to their own country. Our science had its
beginning in Egypt and the first laboratories of which records
have been foimd were in the Temples of Isis. Only priests
were allowed to enter them. However, the systematic study
of chemical changes by means of the balance is compara-
tively a new thing — only a little more than a century old.
During this short time it has proved to be the most impor-
tant business to which men have ever turned their at-
tention. It has revolutionized the conditions of life,
and conferred benefits upon the human race which are
quite beyond calculation.

Definitions

Cube, A solid bounded by six squares.

Octahedron. A solid bounded by eight triangles. It is shaped
like two four-sided pyramids, placed base to base.

Analysis, The separation of a substance into simpler sub-
stances.

SULPHUR WITH SOME FAMILIAR METALS 27

Synthesis. The putting together of two or more substances to
form a new substance of more complicated composition.

Rust, A lustreless, earthy solid, formed by the action of the air
upon a metal.

Galvanize. To coat an iron or steel object with zinc.

Specific Gramty. The quotient obtained by dividing the weight
of anjrthing by the weight of an equal volume of water.

Sulphide. A compound of sulphur with one other element.

CHAPTER III
SOME NATIVE METALS

33. Native Elements. — Of the elements which we have
studied, lead, iron and zinc are found almost entirely in
compounds. Sulphur, mercury and copper are also largely
found as compounds, but they also occur as elements (naiive).
Are there any other elements which have preserved their
separate existence? If so, we may venture the prediction
that they have comparatively little tendency to produce
compounds with other elements. That is, we may expect
them to be inert or inactive, from a chemical standpoint.

We may add to our list of native elements, the metals
gold, silver and platinum. Silver resembles copper and
mercury in being foimd both native and as compounds with
sulphur and other elements. The gold and platinimi of
commerce are derived mainly from the native elements.

34. Gold. — Gold is found in many places, but abimdantly
in few. The chief localities are South Africa (the Trans-
vaal), the United States (Colorado, CaUfomia, Nevada),
British Coliunbia (Klondike), Alaska and Australia (New
South Wales, Queensland). The world's production of gold
has been increasing for many years. Up to 1850 it averaged
only about 27 tons a year. At present it is nearly 700 tons,
valued at about $450,000,000. The Transvaal is first in
the production of gold, and the United States second,
yielding about one-fourth the total production. Australia
has furnished the largest nuggets. One, found in 1858,
weighed 184 pounds, and another (1869) 190 lbs.

35. Different Kinds of Gold Deposits. — Gold may occur
in two ways. (1) It may occur in scales scattered through
the gravel and sand of river-beds and valleys. The gold can
be obtained by a method, the same in principle as the separa-
tion of copper and sulphur, by stirring them with water. The

SOME NATIVE METALS 29

gold (specific gravity 19.3) is far denser than the sand and
gravel (specific gravity about 2.5). A regulated washing
with water will remove the other materials and leave some of
the gold. However, such deposits are worked at present by
the cyanide process. (See §36.)

Or (2) the gold-scales may be distributed through a com-
pact rock, usually quartz. The rock is crushed to a
powder in a "stamp mill" and the powder, mixed to a thin
mud with water, flows over a copper plate which has been
smeared with mercury. The mercury dissolves the gold.
After a time it is scraped ofif and heated. This drives off
the mercury, which is collected and used again, while the
gold remains. The mud which has flowed over the copper
plate still contains nearly half the gold. This is extracted
by the "cyanide process.''

36. The Cyanide Process. — Potassium cyanide is a white,
poisonous solid which smells like bitter almonds and dis-
solves freely in water. Water containing potassiimi cyanide
dissolves gold, but has little or no effect upon the other sub-
stances usually present in gold ores.

The crushed ore, which has flowed off the copper plates,
is placed in large tanks and treated with water containing
one per cent, or less of potassium cyanide. By means of
pumps, the liquid is made to circulate through the tanks.
In 24-48 hours the gold has dissolved and the liquid is
passed through boxes packed with zinc shavings, where the
gold deposits as a black spongy mass, which is afterward
melted. This process is very cheap and efficient. It is
also largely used for sandy deposits like those referred to in
(1) of the preceding section.

37. Properties of Gold. — Gold is bright yellow and nearly
as soft as lead. It is almost twice as dense as the latter.
One gram of gold requires only about half as much heat to
warm it 1** as a gram of silver and only about one-third as
much as a gram of copper. A gold coin, therefore, feels
wanner to the hand than a copper or silver coin at the same

30 AN INDUCTIVE CHEMISTRY

temperature. In other words, gold has a low specific
heat.

When a bit of sulphur is struck with a hammer, it flies to
pieces. But a skilled workman can beat gold into a leaf
only Tiriinr mm. in thickness, so thin that it allows a faint
green light to pass. Closely related to this is the fact that
gold can be drawn into wires of marvellous thinness. A
gram can be made into a wire nearly three kilometers long.

Chemically, gold is inactive. It shows little tendency to
combine with other elements. This is the reason that it is
foimd native. For the same reason it never rusts, but re-
tains its color and luster.

Gold can be distinguished from most metals by the fact
that nitric acid has no effect upon it. In applying this test
to jewelry, it must be remembered that the thin gold layer
on plated objects will protect the substance beneath. The
surface must first be scraped ofif at the point to be tested.
The jeweller draws the suspected object over a black stone
(touchstone), leaving a streak of the metal. He then in-
vestigates the behavior of this streak with nitric acid.

Gold is so soft that it would wear away rapidly in use, so
other metals (copper and silver) are mixed with it to make it
harder. American, German and French gold coins contain
90% gold and 10% copper. British gold coins contain {i
gold and tV copper. In the AustraUan coins the copper is
replaced by silver. The jeweller expresses the fineness of
his gold in " carats." A carat is -^ : therefore pure gold is 24
carats fine. Thus, the British coins are 22 carat and the
American 21.6 carat. 18-carat gold is often used for rings.
This contains 75% of gold. The rest is copper, or copper and
silver. For most other purposes, 14-carat gold is the most
suitable mixture. This is hard enough to stand wear very
well, but it contains enough gold to protect it against tar-
nish (58.33%).

38. The Standard of Value. — Gold is the standard of value of most
civilized nations. For instance, the dollar is defined as a fixed weight

SOME NATIVE METALS 31

of gold, and anyone can take gold to the mint and have it coined by
paying a small fee. The coins are regularly analyzed by chemists and
the utmost care is taken to keep their fineness the same.

39. Silver: Occurrence. — Native copper and gold always
contain silver. Lead-glance usually contains enough to
pay for its extraction (up to 1%). Native silver occurs in
Peru, Mexico, Colorado, Arizona, Montana and elsewhere.
Nuggets weighing several hundred pounds have been foimd.

Silver-glance (silver sulphide) occurs in the same localities.
It often crystallizes in octahedra. It is just about as dense
as lead-glance (specific gravity, 7.3). It is blackish lead-
gray, shining and metallic-looking. The fact that it can
be readily cut into chips with a knife distinguishes it from
most other minerals. Heating on charcoal with the blow-
pipe expels the sulphur and a bead of silver remains.

Silver can be extracted from its ores by the cyanide
process. The method is nearly the same as that used with
gold ores. (See §36.)

40. Extraction of Silver from Lead. — ^We have noticed

that lead-glance is almost sure to contain more or less silver

as an impurity. This silver goes into the crude lead which

is made from it. It is extracted by melting the lead in an

iron kettle and stirring up with it 0.5%-1.5% of zinc. A

layer forms on the surface and is skimmed off as it freezes.

This layer contains almost all the silver.

The melted lead is treated with a fresh quantity of zinc to extract
the rest of the silver. It is very much better to use the zinc in two
separate portions than to put in a double quantity in one operation.
Let us work out an example. Suppose that the lead contains 1% of
silver and that one treatment with zinc wiU extract A of the silver
which is in the lead. Then each treatment will divide the percentage
of silver in the lead by 10:

After one treatment it will contain 0.1%

After two treatments it will contain 0.01%

After three treatments it wiU contain 0.001%

Three treatments give a practically complete extraction. A triple
quantity of zinc in the first operation would do nothing of the sort.
This principle is of great importance.

32 AN INDUCTIVE CHEMISTRY

41. Basis of the Method. — ^Two facts form the foundation
of this method: (1) when melted zinc and melted lead are
stirred up, the two liquids do not merge into one, like alco-
hol and water, but, like oil on water, the zinc goes to the
top as soon as the stirring is stopped; (2) silver dissolves
much more freely in melted zinc than in melted lead, so that
the zinc, when it goes to the top, takes the silver with it.

42. Physical Ftoperties of Silver. — ^Pure silver is white
and will take a high polish. It conducts heat and the electric
current better than any other substance. It is not used for
electric wires because it is too expensive. Copper conducts
about nine-tenths as well and is vastly cheaper. The
specific gravity of silver (10.5) shows that it is heavier than
copper, but lighter than lead. It can be beaten into ex-
ceedingly thin foil and a gram of it can be drawn into a wire
2 kilometers long, so that it approaches gold in malleability
and ductility. Silver can therefore be readily worked into
the most various shapes for ornamental objects.

43. Chemical Properties of Silver. — ^When silver is heated
to 960*" (a clear yellow heat) it melts. Heating to a much
higher temperature causes the liquid to boil, giving the
vapor of silver. By leading this vapor into a cooler vessel
to condense it, very pure silver can be obtained. Vessels
of lime must be used, since most other materials would melt.
Jean Servais StaSy the great Belgian chemist, prepared silver
of extraordinary purity in this way. He informs us that
the vapor is blue and that some of it escaped into the labora-
tory, making the air cloudy, and giving it a metallic taste.

In pure air, silver does not rust. The tarnish which ap-
pears on the silver of the household is due to compounds of
sulphur in the air, which come from the burning of coal and
gas, both of which contain small quantities of sulphur com-
pounds. The tarnish is a film of silver sulphide. The
same film forms on spoons that are used with eggs or mustard,
both of which contain sulphur compoimds. The misleading
term ''oxidized silver'' is applied to silver which has been

SOME NATIVE METALS 33

artificially covered with a dark layer of silver sulphide.
Silver coins carried loose in the pocket are often tarnished by
the sulphur compounds of the perspiration.

Silver differs from gold and platinum in being attacked
and dissolved by nitric acid.

44. Uses of Silver. — The silver of commerce always con-
tains copper added to harden it. Sterling silver contains
92.5% of silver and 7.5% copper. The silver coinage of
Great Britain has the same composition. That of the con-
tinent of Europe and of the United States contains 90%
silver and 10% copper. Mirrors are made by depositing a
layer of silver on glass.

From 1800 to 1850 the world's production of silver was
about 650 tons a year. At present the total output is nearly
6700 tons, of which the United States and Mexico together
furnish about two-thirds. Canada and Australia produce
most of the remainder. The chief silver-producing states
are Montana, Utah, Colorado, Nevada and Idaho.

45. Platinum. — In alluvial deposits of sand and gravel,
in the Ural Moimtains, are foimd heavy, steel-gray, shining
scales which flatten out when struck with a hammer. Their
specific gravity (nearly 20) is so much above that of the
other particles present that they are easily separated by
washing. They consist of plaiinuniy mixed with five other
metals which are much like it.

Platinum somewhat resembles silver, but it has a gray
luster and is much harder. Its specific gravity (21.5) is
more than twice that of silver and it melts at a very much
higher temperature (1775**). The air has no effect upon it
at any temperature. Nitric acid does not act upon it. It
can be welded at a red heat.

Platinirai does not soften or melt in the flames commonly
used in the laboratory and most chemicals do not affect it,
for it is a very inactive metal. For these reasons it is made
into crucibles, dishes, wire and foil for the use of chemists.
However, there are substances which do act upon it and

34 AN INDUCTIVE CHEMISTRY

which must not be heated m platmum vessels. Among these
are metals, like lead, copper and zinc, which would melt
with the platinum and ruin the vessel.

When heated, platinum expands at just about the same
rate as glass. Hence a platinum wire, sealed through a
plate of glass, does not crack the gla^ around it when the
junction is heated or cooled. The wires which pass through
glass tubes to convey the electric current in lecture-table
apparatus are always platinmn. Two short platinum wires
carry the current into and out of the bulb in the incandes-
cent lamp. like gold, platinum is not at all acted upon by
the Uquids of the mouth, and it is more tenacious than gold.
These facts have led to its use by dentists. Platinum, when
set free from some of its compounds, takes the form of a
velvet-black powder called platinum black. This also has
some important uses which we shall study later. The price
of platinum varies greatly. It has tripled within the last
twenty years and the metal is now more expensive than gold.

46. The Platinum Metals. — ^The five metals which occur with plati-
num resemble it and are classed with it imder the title ''platinum
metals." We can only mention two of them.

Osmium is interesting because it is the densest of all substances
(specific gravity, 22.5) and one of the most difficult to melt. This last
fact led to its use as the filament of the osmium lamp, which was very
promising for a time, but which has been displaced by the timgsten
lamp.

Iridium is white and almost as dense as osmium. It is very hard
and communicates its hardness to platinum when mixed with it. Grold
pens are tipped with a mixture of these two metals since the tips must
be hard and must resist the action of the acids usually present in ink.
The same material is used to make government standards of weight and
length. It is just as unalterable in the air as platinum, and being much
harder, it is less afifected by mechanical wear.

Related Topics

47. Base and Noble Metals. — Lead, copper, iron and zinc
rust in the air rapidly, when heated. The products are dull
earthy powders, not tough like the metals, and quite incapable of

SOME NATIVE METALS

being beaten into foil or drawn into wire. The early chemists
called these substances "calces" (singular, calx), but they are
now called "oxides." About the middle of the 17th century
two particularly keen minds, the French physician Jean Rey
and the English chemist Mayow, grasped the fact that the oxides
always weighed more than the metals from which they were made.
They explained this by supposing that during the heating
something wa^ added to the metal from the air. But the suggestion
attracted little attention at the time and it was not till a cen-
tury and a half later that Lavoisier followed it up systematically
and showed that it was in fact the correct explanation.

Gold, silver and platinum are not converted into oxides when
heated. They were called the noble metals, because they re-
sisted the action of fire, and the others which yielded to it, and
were cheap and abundant, were called base metals. Mercury
stands on the border-line. It does not rust in the cold, but when
heated gently in air, it is slowly changed to a red oxide. At a
higher temperature, the oxide again yields the metal.

48. Alloys. — Materials which are composed of two or more
metals are called alloys. The coinage metals, sterling silver
and jewellers' gold, are examples. Here are some of the more
important alloys. The composition is expressed in percentages.

Copper

Zinc

Tin

Lead

NiOKEIi

Brass

Gun-metal

German Silver

Solder

Bronze (Coinage)

Pewter

Nickel Coins

49. Nature of Alloys. — Are alloys to be classed as solutions, as
compounds or as mere mixtures? This question must be answered
for each alloy separately. Silver-copper alloy (silver coinage)
seems to consist merely of crystals of copper and of silver lying
side by side. It is a mixture. Silver-gold alloys appear to be a

36 AN INDUCTIVE CHEMISTRY

homogeneous solviionoi the two metals. Gun metal contains a
definite chemical compound of copper and tin.

Many familiar facts show that some alloys cannot oe classed
as mere mixtures. Thus, the nickel coins, which contain 75%
of copper, are white. If they were mixtures, they would be
nearly as red as copper; 30% of tin added to copper, makes it
completely white. Silver may contain as much as 30% of
gold without showing any yellow color. The specific gravity of
alloys is usually greater than the figure calculated from their
composition, assuming that the metals are merely mixed. The
ability of an alloy to conduct the electric current is very much
less than that calculated from the conducting powers of the
metals when separate. Often the alloy is a poorer conductor
than either metal in it. This is the reason why copper for
electric wires is so carefully purified from every trace of other
metals.

Definitions

Metal. An element which is more or less ductile, malle-
able and tenacious, and which has the peculiar luster which
we associate with substances like copper, silver and gold.
(See Chap. XXIX.)

Non-metal. An element which, like sulphur, has none of
the properties of a metal. (See Chap. XXIX.)

Inactive. Inert; indisposed to take part in chemical changes.

Specific Heat. The quantity of heat required to warm one gram
of a substance one degree.

Touchrstone. A black stone used by jewellers in testing metals.

Malleable. Capable of being beaten out, under the hammer, into
thin foil.

Ductile. Capable of being drawn out into fine wire.

Tarnish. A film of rust on a metal, destroying the luster

Alluvial. A term applied to deposits made by the action of
streams.

Calx. A lusterless, earthy solid, produced by heating a metal in
the air.

AUoy. A material composed of two or more metals

CHAPTER IV

ANOTHER NATIVE NON-METAL: CARBON

50. Diamond: Occurrence. — In 1870 the children of a
South African farmer in Griqualand, on the border of the
Orange Colony, were playing with some small bright pebbles
which they had picked up. The stones attracted the atten-
tion of a miner, who perceived that they were diamonds.
Thus were discovered the Kiniberly Diamond Mines, the
most important of which could all be included in a circle three
miles and a half in diameter. Out of this little area has come
perhaps a billion dollars' worth of gems.

Each mine is a small oval about 200 meters in diameter.
The surface is yellow weathered material. Below this is a
soft blue-green rock (serpentine) in which the diamonds are
found to the extent of about 6 carats per cubic meter (1
carat = about 0.2 gram). Occasionally it happens that a
diamond flies to pieces after being taken out of the rock.
This looks as though the gems had been formed under pres-
sure and, in fact, everything indicates that they were pro-
duced at a great depth and brought to the surface by a
volcanic outflow.

51. Properties of the Diamond. — ^The diamond crystal-
lizes in octahedra and in other forms. The stones worn as
gems are not crystals. They are "brilliants,'' cut in such a
way as to display the "fire" to the best advantage. The
luster of the diamond is due to its enormous refracting power
and to the fact that the refracting power is not only very
great, but also very different for different colors, so that at
one angle one gets a glint of red, at another of green, and so
on. Its specific gravity is 3.5. It is the hardest of minerals,
that is, it scratches all others and is scratched by none. It
is inactive chemically, and is not at all affected by any liquid
at ordinary temperatures. There are a few solids, like wash-

4 37

38 AN INDUCTIVE CHEMISTRY

ing soda for instance, which when melted with a diamond at
a red heat, will destroy it.

52. Preparatioa of Diamonds in the Laboratory. — The dia^
mond has been made artificially from charcoal, by the great
French chemist, Henri Mois-
san. He heated a mixture of
charcoal powder and iron
to a very high temperature
(3000°), in a furnace heated
Fio. io..-Du«tani of Mouaan . (uraaoB. ^y an elcctric arc (Fig. lOb).
The melted iron dissolved
some of the charcoal. The vessel was then taken out of
the furnace and plui^ed into water (Fig. 11), The result
was to form a crust of
iron on the surface, which
exerted a powerful pres-
sure on the liquid in-
terior. The experiment
imitates, in a small way,
the formation of dia-
monds in nature, where
the pressure is due to ^

, , Fia. lOo. — Mouaan a funuice in operation.

overlying rock-masses.

When the iron is dissolved away by acids, it is found
that some of the charcoal has been converted into little
diamonds. Some of them are shown
in Fig. 12, Their small aze (0.5 mm.
in diameter) renders them of no com-
mercial value.

53. Uses of flie Diamond.— The
color of natural diamonds varies from
white through yellow and brown to
black. Only the pink, blue or color-
less specimens are esteemed as gems:
even a slight tint of yellow detracts
FiQ. ii.-c«iUiie tha crucible, greatly from the value. The bla^k

ANOTHER NATIVE NON-METAL: CARBON 39

Fig. 12. — ^Artificial diamonds.

diamonds, most of which come from Bahia, Brazil, are largely
used as an abrasive, for glass-cutting, for the cutting surfaces
of rock-drills and the like.

Some very large gems have been obtained from the South
African mines. The largest was the '^Cullinan,'' found in
the Premier mine on Jan. 25th,
1905, and presented to King
Edward on the 66th anniver-
sary of his birth. It weighed,
before cutting, 3034| carats
(20 oz. Troy, or more than 1
lb. 5 oz. Avoirdupois) . A black
diamond weighing over 3000
carats (600 grams) was found
in Bahia in 1895.

54* Graphite : Occurrence
and Properties. — Graphite^ also
called plumbago and black had,

is mined at Byers, Chester Co., Pa., at Ticonderoga and
Hillsdale in New York, and elsewhere in the United States.
Much graphite comes from Ceylon and perhaps the finest
of all lead pencil graphite is brought from the mines of
Eastern Siberia.

Graphite occurs in flat, six-sided crystals and in large
masses which have no distinct crystalline form. It is
blackish lead-gray, greasy to the touch and (like lead) it
leaves a black mark on paper. Hence the name "black
lead,'' though graphite contains no lead. Unlike the dia-
mond, it is one of the softest of minerals, being easily
scratched with the finger nail. It is less dense than the
diamond, having a specific gravity of about 2. It differs
also from the diamond in being a conductor of the electric
current. It is very inactive chemically.

55. Uses of Graphite. — ^Like diamond and charcoal, graph-
ite has never been melted. This causes it to be largely
used when extreme resistance to heat is desirable. Crucibles

40 AN INDUCTIVE CHEMISTRY

for melting metals are made of a mixture of graphite and fire-
clay. The "lead" of pencils is a mixtm^e of finely powdered
graphite with fine clay carefully freed from grit. The hard
pencils contain less graphite and more clay than the soft.
Graphite is employed as a lubricant where oil, for some
reason, will not answer, for instance in the chains of
bicycles and automobiles where oil would take up dust.
Stove polish is made of graphite and soap. Graphite
makes excellent paint. The electrodes which carry the
electric current into and out of electric furnaces are often
made of graphite.

56. Carbon. — When graphite or diamond is intensely
heated in the air, it bums away. If the air is excluded,
graphite is not afifected by heat, but diamond swells up and
turns to graphite. Nothing is added or removed in this
change; the weight of the graphite is the same as that
of the diamond heated. Neither graphite nor dia-
mond has ever been separated into simpler substances.
When they are burned in the air the product is a
gas which, if collected, weighs 3f times as much as the
diamond or graphite taken, showing that something from
the air has been added. Both yield the same substance.
These facts show that graphite and diamond have some-
what the same relation to each other as «- and i^-sulphur.
They are two forms of the same element, carbon}
Anything which can be converted into graphite or
diamond without loss in weight must also be a form of
carbon.

57. Forms of Carbon not Found in Nature. — Using this
test we can at once class as varieties of carbon three impor-
tant artificial products. These are charcoal, coke and
lampblack. All three change into graphite at very
high temperatures without alteration in weight. All

* In speaking of such forms the adjective aUotropic is in common
use. It has about the same meaning as the more familiar word "dif-
ferent."

ANOTHER NATIVE NON-METAL: CARBON 41

three differ from graphite and diamond in being amor-
phous. They do not conduct the electric current nearly
as well as graphite. They are not pure carbon. Char-
coal and coke may contain 10% or more of impurities
which remain, as ash, on burning the charcoal or coke
in the air.

58. Charcoal. — ^We already know how wood behaves when
heated in the air. The effect of heat in the absence of air
we can learn by filling a test tube one-third with sawdust, or
bits of wood, and heating slowly. Gases escape which can
be lighted at the mouth of the tube, where they bum with a
bright yellow flame. (Wood gas was used in one of the
earliest attempts at gas-lighting in 1801, when M. Lebon
lighted his estate in France with it. It has never amounted
to anything practically, because better gas can be
made more cheaply from coal.) Tarry liquids appear
in the cooler part of the tube and charcoal remains in
the bottom.

59. Manufacture of Charcoal. — ^In the manufacture of
charcoal on a large scale, a large horizontal iron cylinder is
used. The wood is heated by outside coal-firing for twelve
hours. The liquid products are led away by tubes from the
cylinder and collected, for they contain substances which
find a ready market. Among these are wood alcohol (used
in the manufacture of varnish and for many other
purposes) and acetic a^dd (the substance which gives
vinegar its sour taste. Vinegar is not made from the
acetic acid of wood, but the latter has many uses in
chemical industry).

60. Properties of Charcoal. — Charcoal floats on water, but
this is because it is extremely porous. Its real specific gravity
varies from 1 . 5 to 2 in different specimens. A high temper-
ature in the preparation makes the charcoal gray-black,
dense, a better conductor of the electric current and more
difficult to ignite. Charcoal made at a low temperature is
dead black or brownish and so inflammable that it sometimes

42 AN INDUCTIVE CHEMISTRY

ignites when removed from the cylinder in which it
is made.

6i. Conversion of Charcoal into Graphite. — Evidently the
high temperature charcoal resembles graphite more than the
low temperature charcoal does. Electric light carbons are
made of a dense kind of carbon obtained from the gas works.
The examination of a burnt-out carbon shows that the end
which has been in the arc is soft, gray, metallic and greasy
to th3 touch. The very high temperature (4000°) has changed
the heated portion to graphite. The filament of an or-
dinary incandescent lamp is charcoal when the lamp is new.
But, on opening a lamp which has burnt out it is found that
the filament has been converted into graphite. Probably
there will also be a film of graphite on the inside of the glass,
which may have cut off a good deal of the light before the
lamp gave out completely.

62. Carbon Vapor. — Two important conclusions follow.
First, carbon, although it cannot be melted, can be converted
into vapor. For this is the only way in which it could. be
transported from the filament to the glass of the incandescent
lamp. Second, when the vapor is cooled, graphite is
formed.

Moissan established the truth of both these statements by
many beautiful experiments with his electric furnace (Fig.
10). Thus, a crucible and cover, made of charcoal, were
completely changed into graphite in three minutes. But the
crucible held its shape perfectly and the cover did not stick,
as it would have done if there had been any melting. He
heated charcoal in an electric furnace in which there was a
copper tube, kept cold by a rapid current of water passing
through it. The cold surface of the copper cooled and con-
densed the carbon vapor, produced by the heating of the char-
coal, and graphite crystals were the only product. He never
obtained the slightest evidence of melting of the charcoal or
the graphite. Remembering that the change of one modifica-
tion of carbon to another takes place only at the highest

EENBI MOISSAN
B. Paris, Sept. 28, 1858,

ANOTHER NATIVE NON-METAL: CARBON 43

temperatures (say 4000°) we can state the facts as
follows:

Graphite is formed when any other modification of carbon
is heated.

Graphite at the temperature of the electric arc passes di-
rectly into carbon vapor vnthxmt melting.

Carbon vapor, when cooled, produces graphite, no liquid
carbon being formed,

63. Coke. — Coke bears the same relation to soft coal (bi-
timiinous coal) that charcoal does to wood. It is made by
heating soft coal, away from air, imtil everything which can
be driven off by heat has escaped. This is done in furnaces
which may be 10 meters long, 2 meters high and 0.5 meter
wide, and which are heated from the outside by nimierous
Bunsen flames. The furnaces are made narrow, so that the
heat can penetrate to the center of the mass. The flames are
fed by the gas from previous charges, which is stored in gas-
holders; the process yields more gas than it consumes, so that
a surplus is available for other purposes. The valuable prod-
ucts which escape are led off through tubes and purified.
Among them are illuminating gas (used about the plant),
ammonia water, benzene, creosote (excellent for protecting
wood against decay), carbolic acid (disinfectant), tar-cam-
phor and pitch. Coke is gray-black and is harder and denser
than charcoal. It is the great fuel of the iron industry, and
is made in enormous quantities for use in the blast furnace.

When a mixture of 97% of coke with 3% of iron-filings is
heated in an electric furnace, the coke is changed to graphite.
Two heavy carbon rods carry a current into opposite ends
of the mass. Between them the current, which is a strong
one, passes through the coke and, since it is a bad con-
ductor, a very high temperature is produced. The change of
coke to graphite is due entirely to the high temperature; the
current serves only as a means of supplying heat. The
change is accelerated by the iron, but the latter finally

44 AN INDUCTIVE CHEMISTRY

vaporizes, so that the finished product is free from
iron. The graphite is much purer than the coke,
because the impurities, which usually remain as ash
when coke is burned, are driven off in vapor by the in-
tense heat.

64. Lampblack. — ^Lampblack is nothing but pure soot.
We can easily make some by holding a bit of crayon in the
yellow flame of the burner. On a large scale, the best
grade of lampblack is made by a method the same in prin-
ciple. A circle of flames burning from a horizontal perforated
iron gas-pipe strikes the lower surface of a circular cast-iron
vessel which rotates slowly on a vertical axis. The vessel is
kept full of running water, to cool it. A scraper automatic-
ally removes the lampblack as it collects. Because of its
cheapness, natural gas is used in this process. Lampblack
is also made by burning substances like rosin, turpentine
or petroleum in such a way that the air supply is insuffi-
cient and therefore much soot is produced. The smoke is
led through chambers in which the lampblack deposits on
the walls, or on cloths hung up for the purpose.

Lampblack is a velvety, jet-black powder, which shows no
trace of crystallization. Its specific gravity is about 1.8
but varies in different specimens. The temperature of the
electric furnace transforms it into graphite. It is used in the
manufacture of printer's ink, India ink and shoe-polish.
Since it is entirely unafifected by the weather, it makes ex-
cellent black paint.

65. Coal. — Pure carbon, when heated in the air, burns
away completely. Coal cannot, therefore, be pure carbon.
Pure carbon, heated in the absence of air, is unaltered at a
yellow heat. Therefore the soft or bituminous coals, which,
when heated, give off 15-50 per cent, by weight of various
substances, leaving a residue of coke, must be very different
indeed from pure carbon. However, carbon is the chief
constituent of all coals, and their value as fuel depends
largely upon this fact.

ANOTHER NATIVE NON-METAL: CARBON 45

The two chief varieties of coal are anthracite and bi-
tuminous. Here are some of the properties of both:

Properties of

Anthracite and Bituminous Coal

Anthracite

Bituminous

Luster

bright, ahuost metaUic

greasy to pitchy

Specific Gravity

1.5

1.3

Tenacity

tough

fragile

Flame

pale-blue

yellow, smoky

Effect of heat in ab-

sence of air

almost unaltered

forms coke (see above)

Percentage of free

carbon

85-93

60-70

Percentage of ash

10 (varies greatly)

10 (varies)

66. Importance of Coal. — The world's output of coal
each year is about a bilUon tons and this enormous figure is
a striking proof of the relation of this form of carbon to
modem life. Civilization is based upon it. Its energy
warms and lights our homes, drives our machinery and
transports us over land and water.

How long the coal supply will hold out is an interesting question.
The estimates of geologists range from one centiuy to ten. The
amount mined is constantly increasing. Unless some substitute is
found, there will be a radical change in the conditions of life when the
coal is gone.

Our methods of utilizing coal are extremely crude. The waste be-
gins at the mine, where the coal is taken out in such a way that much
of it can never be mined at all. A good modern steam engine converts
only about one-tenth of the total energy of the coal into useful work.
In lighting by electricity less than one per cent of the energy of the coal
is converted into light. The fraction which is usefully employed in
ordinary cooking can hardly be greater. One third of the ashes
discarded by the average household consist of unbumt coal. Such
losses would not be tolerated in any other line of work.

46 AN INDUCTIVE CHEMISTRY

67. Carbon Disulphide. — Having studied carbon and sul-
phur separately, it will be of interest to learn something
about the compound of the two. Here again we notice an
abrupt change of properties, for carbon disulphide is quite
unlike either of its constituents. It is a colorless liquid,
which passes easily into a vapor. Prolonged inhalation of
the vapor is injurious. When the liquid is poured into water,
a trace dissolves, but nearly all of it forms a layer below the
water. Prom this it follows that its specific gravity is greater
than that of water. When stirred up with alcohol, carbon
disulphide forms a homogeneous liquid, no matter what pro-
portions of the two liquids are taken.

Carbon disulphide is very inflammable. Its vapor takes
fire at a temperature (120°) only a little above the boiling-
point of water and great care is required in handling it.

We have seen that carbon disulphide dissolves sulphur.
It also dissolves rubber and is used in the vulcanizing proc-
ess. It dissolves oils and fats and is employed in extracting
them from substances like olives and palm kernels. It is
destructive to moths and other insects and to fungi. Para-
sites which attack the roots of plants can be destroyed by
pouring a little carbon disulphide into a hole near the plant
and then plugging the hole to prevent the liquid from
evaporating. Care is necessary, for too much carbon disul-
phide will injure the plant.

68. Formation of Carbon Disulphide. — Carbon disulphide
is obtained by the interaction of sulphur vapor and red-hot
charcoal in a closed furnace, electrically heated. Graphite
rods carry the current through the walls of the furnace and
the space between these rods is filled with pieces of coke.
The space above contains the charcoal and sulphur. When
the current passes through the badly-conducting coke, a
high temperature is produced (see artificial graphite, p. 43).
The sulphur is vaporized and the charcoal becomes red-hot.
The two combine and the carbon disulphide vapor is led
away and, by cooling, converted into a liquid (condensed).

ANOTHER NATIVE NON-METAL: CARBON 47

Definitions

BriUiant, A shape into which diamonds are often cut, to display
the luster.

Carat, A unit of weight, used by jewellers for diamonds and
other gems. One carat =0.205 gram. The diamond carat must
not be confused with the carat used to express the fineness of ^old.
(Chap. III.)

Allotropic. A term applied to two forms of the same
element, differing in properties.

Filament, The solid thread which serves as a source of
light in the incandescent lamp.

CHAPTER V

THE ATMQSPHERE: A MIXTURE OF NON-METALLIC

GASES

69. Weight of the Air. — ^The fact that the air is a real
substantial thing is sufficiently shown by its destructive
effects when put into rapid motion during storms. Being
material, it must have weight, and this is easily proved, even

with the roughest balance. Fig. 13 repre-
sents a liter flask closed by a stopper carrying
a short glass tube. This tube connects with
a piece of rubber tubing which can be closed
by a clamp. The apparatus is weighed, the
air removed by an air-piunp and the clamp
closed. Reweighing will show a loss amount-
ing to about 1.2 gram. A loss only rirlinr as
great could easily be detected with a fairly
good balance. By a careful experiment of
this kind, it can be shown that a liter of air
measured at 0"*, the melting-point of ice, and
when the barometer stands at a height
of 760 mm., weighs 1.293 grams. Since a
liter of water weighs 1000 grams, the specific gravity of air
is iiW or .001293 (about t^^).

Roughly, we may say that water is about 800 times as
dense as air; yet the total weight of the atmosphere is
enormous. Stated in kilograms, it is represented by the
number 52 followed by seventeen ciphers. This is usually
written thus: 52 X 10^'. The expression has exactly the
same meaning as the number written out in full, and it
saves much space and confusion.

70. Pressure of the Air. — ^At the surface of the earth, the
average pressure of the air is equal to 1033 . 6 grams (more

Fig. 13.— Appara-
tus for determin-
ing the weight of
a liter of air.

THE ATMOSPHERE 49

than the weight of one kilogram) on every square centimeter
of the surfaces exposed to it. This corresponds to about
14.6 pounds per square inch. It is known as the pressure
of one ntmosphere. The total weight of the air is obtained
by multiplying 1033.6 g. by the area of the earth's surface in
square centimeters.

71. Chemical Study of the Air. — Among the laboratory
studies is one in which we heat iron, copper and tin in the
air. The facts established in that exercise furnish the
starting-point from which we shall attack the problem of the
chemical nature of our atmosphere. Let us recall them:

(1) The metals are converted into lusterless powders,
called oxides.

(2) Air is essential to the change, for heat alone fails to
produce it.

(3) The oxide always weighs more than the metal from
which it is made.

How much are we entitled to infer from these three facts?

(a) From (1) it is clear that the change from metal to
oxide is chemical, since there has occurred in each case that
abrupt change of all the properties of the metals which we
have learned to regard as the sign of a chemical process.

(b) Taken together (2) and (3) give ground for the con-
clusion that something has been added to the metals from the
air. In other words, the air contains something which com-
bines with the metals in the same way as sulphur combined
with them in the laboratory study of the formation of sul-
phides.

The next question is whether the air consists wholly, or
only partially, of this substance, and the way to answer it
is to heat a metal in a confined volume of air and see whether
all of the air, or only a portion, disappears when the oxide
is formed.

72. Class-room Experiments. — (a) Fig. 14 represents the
apparatus for a preliminary experiment. A horseshoe mag-
net is hung over a glass rod in a bell jar. Bits of rubber tub-

AN INDUCTIVE CHEMISTRY

Fio. 14. — Action of heated iron on air.

ing slipped over the ends of the rod, and crowded against the
jar, hold the rod. A supply of iron powder clings to the
poles of the magnet. The open end of the jar dips into
water. The burning of the iron is started by a red-hot wire

introduced through the
neck of the jar. Then
the stopper is replaced.
The iron bums feebly
for a time and then
goes out, much sooner
than it would in the
open air. The level of
the water inside the jar
rises. The jar is trans-
ferred from the shelf
to the bottom of the
trough, the stopper re-
moved and a biuning splint inserted. The flame is extin-
guished at once.

(b) Place some iron powder in a porcelain crucible and
wet it. Float the crucible in water and invert a small grad-
uated cylinder over it (Fig. 15). Let
stand for a week or more, noting the
level of the water. There is a gradual
rise, which ceases when about i of the
air has disappeared. The gas which
remains extinguishes a flame.

(c) Quantitative knowledge can be ob-
tained by the apparatus shown in Fig.
16. C, is a graduated cylinder, which is
full of air when the experiment is begun. Fio. is.— Rusting of iron
C, is a similar cylinder full of water. ^^ ^."^^"^ ''^^^^
A liter of water is allowed to drop

slowly into C^; the displaced air passes^over a column of red-
hot copper-clippings before being collected in C^. If the
work is well done, 790 c.c. of gas will collect in C,. Some of

THE ATMOSPHERE

the copper in the tube, especially in the end toward Cj, has
turned black. If the gas is made to pass through the tube
a second time, there is no further loss in volume. The gas
collected is odorless and extinguishes flame. But if the
cylinder is allowed to stand open on the desk for a few
moments a flame will bum in it, showing that it is now
full of air. The rapid escape of the gas upward proves that

wu \7y

• • •

M H

Fia. 16. — ^Action of red-hot copper on a measured volume of air.

it must be lighter than air. A quantitative experiment like that
indicated in Fig. 16 shows that a liter of it weighs 1.25 grams.
73. Nitrogen. — ^Aristotle and, following him, the whole
ancient and mediaeval world, considered the air as a simple sub-
stance. Our experiments show that this opinion was not correct
and that it contains at least two things, one of which acts on
metals while the other does not. The one which does not is
called nitrogen. It is an element We have obtained it in
the experiments of the preceding section, especially (c).
This nitrogen is not pure, but the impurities in it are small in
amount and we shall not fall into any error by using it as a
basis for our study of the element. We can prepare it in
the laboratory in purer condition, not from the air, but by
setting it free from one of its compounds.

62 AN INDUCTIVE CHEMISTRY

74. Properties of Nitrogen. — Most of the important facts
about nitrogen may be learned from the laboratory or class-
room experiments. It is a colorless, odorless gas, lighter
than air. Since it can be collected over water, its solubility
in that liquid must be slight. Like all gases, it has been
condensed to a liquid by intense cold and pressure, and the
liquid has been frozen to a solid. Liquid nitrogen looks
like water. It forms when the gas is cooled to -194°. The
liquid freezes to a white solid at -214**.

Since nitrogen does not combine with any of the metals we
have used, there is some basis for the conclusion that it is
an inactive non-metal; much less active than sulphur, for
instance. But on this point a wider study of the element is
needed, which would, on the whole, confirm this conclusion.
At the same time, it would show that there are elements with
which nitrogen combines readily. One of these is the
metal magnesium with which the student is perhaps famil-
iar, on accoimt of the extensive use of its brilliant flame as a
source of light for photography. The compound of mag-
nesium with nitrogen is made by passing the gas over the
hot metal, in apparatus similar in principle to that described
in § 72 (c). Mercury is used instead of water. The com-
pound is a yellow powder, called magnesium nitride, for the
same reason that the compound of copper and sulphur is
called copper sulphide. Impure magnesium nitride can be
formed by simply heating a mass of powdered magnesium
in the air on an asbestos plate.

Nitrogen is not at all poisonous, but it will not support
life. A mouse, placed in it, dies by suffocation.

75. The Second Chief Constituent of the Air. — So far,
our experiments prove that the air consists chiefly of two
elements, nitrogen, and another element. To the second
element, Lavoisier, in 1775, gave the name which it still
bears, oxygen. Oxygen unites with the metals and the
compounds formed are the oxides. Since a burning bit of
wood is extinguished in air which has acted upon heated

THE ATMOSPHERE

copper or iron, it would seem that oxygen is also responsible
for ordinary burning.

The next task is to determine the properties of oxygen, and
to do this it is necessary to prepare it in pure condition. As a
raw material the oxides suggest themselves at once, for they
are the only substances we have yet met (the air excepted)
which certainly contain oxygen. Our problem, then, takes
the form of separating an oxide into its two elements, (1)
the metal and (2) the element of which we are in search.
How is this to be done?

We have seen (p. 13) that heat drives off sulphur from
pyrite. This, together with what we have learned about the
action of heat upon wood and soft coal, gives some basis for
the idea that high temperature is likely to have a separating
or decomposing
action upon
compounds.
Heating the ox-
ides might af-
ford the solu-
tion of the
problem.

76. The Ox-
ide of Mercury.
— ^Now the ox-
ides of iron and

copper can be decomposed by heat, but the temperature re-
quired is so high that the experiment cannot be performed
with inexpensive apparatus.

When mercury is heated in the air, it slowly passes into a
dense red powder, which has been known since the middle of
the 14th century, and is used in medicine and as an insecticide.
This is the oxide of mercury. Since it can be purchased in pure
condition, it is not necessary to make it.

Some mercury oxide is heated in the apparatus shown in

Fig. 17. The vessel is called a retort It should be made
5

FiQ. 17. — Heating the oxide of mercury.

64 AN INDUCTIVE CHEMISTRY

of hard glass, so as not to soften when heated. It is con-
nected with a bulb to receive the mercury which we anticipate
as one product, and the apparatus is so arranged that any gas
set free will be collected in an inverted bottle filled with
water.

The red powder completely disappears, if the heating is
continued long enough. A metallic liquid, which we rec-
ognize as mercury, appears in the bulb. A colorless gas
bubbles up through the water and collects in the bottle.
This can only be the other constituent of the oxide. A splint
bearing a spark bursts into flame when plunged into the gas
and bums much more vigorously than in air. This gas is
the element oxygen.

77. Properties of Oxygen, — Mercury oxide is rather ex-
pensive and, for further investigation of oxygen, it will be
cheaper and save much time to use a cylinder of the com-
pressed gas. Two bottles of the same size are filled over
water with oxygen. One is placed right side up on the table
and the other is placed on a ring of the stand with the mouth
down. In a few moments both are tested with a splint bear-
ing a spark. The gas in the inverted bottle does not aflFect
the spark, while, in the other, the wood bursts into flame.
The gas, then, is heavier than air. A quantitative experiment
with the apparatus of §69 shows that a liter of oxygen at 0°
and under a pressure of 760 mm. weighs 1 .43 grams. We per-
ceive that the gas is colorless and, from the fact that it is
collected over water without noticeable loss, we reason that
its solubility in that liquid must be small. At -183° oxygen
condenses to a light blue liquid slightly denser than water,
and, on further cooling, the liquid freezes to a pale blue solid.
Liquid oxygen is strongly attracted by the magnet. This is
a surprising fact, for magnetism is distinctly a property of
certain metals, like iron and nickel, and oxygen is one of the
most non-metallic of the elements.

78. Chemical Properties. — A simple method of ascertain-
ing the behavior of oxygen with various substances is shown

THE ATMOSPHERE 55

in Fig. 18. The substance is placed in the bowl of the iron
spoon, heated until it begins to bum, and then plunged into a
bottle of the gas. In this way it can be shown that zinc
and iron bum in oxygen and that the products are the
same as those obtained by burning the same
metals in the air, that is to say, zinc oxide
and iron oxide. The experiment can be varied

by making a heap of the powdered metal on an • \ i (j ^

asbestos plate^ letting a burner flame play upon r ) ^

the heap till it glows and then directing a

stream of oxygen from the cylinder upon the

metal by means of a glass tube. Iron, zinc

and some other metals bum vigorously to their

oxides when treated in this way. Energetic

burning of this kind, accompanied by the escape Fiq. is. — Com-

of light and much heat, is called combustion, ^^^^ ^ °^'

Sulphur, heated in a spoon, bums languidly
in the air, but in oxygen the combustion becomes energetic.
The product is a colorless gas with a sharp suffocating odor,
which must, of course, be an oxide of sulphur.

If we went through the list of the elements, trying the
behavior of all of them with oxygen, we should find a few,
like gold, platinum and some others, upon which the gas has
no action. But most of them would imite with it, either
rapidly, Uke those just mentioned, or slowly. Oxygen, then,
is a very active element.

Free oxygen is essential to the life of animals. In its
absence, death by suflFocation results, even when the gas in
which the animal is placed is non-poisonous. It is also es-
sential to the Ufe of the ordinary plants. Some simple
plants (fungi and micro-organisms) are able to live without
it.

79. The Air a Mixture. — ^We are now ready to take up
the important question whether the nitrogen and oxygen of
the air are chemically combined or merely mixed; whether the
air is a mixture or a chemical compound of the two gases. This

56 AN INDUCTIVE CHEMISTRY

•

question can be answered with practical certainty by com-
paring the properties of oxygen and nitrogen, on the one
hand, with those of air on the other. The properties of
air are those of oxygen modified by those of nitrogen. Thus
the air supports the combustion of substances in the same
way as oxygen does, but less energetically, because the nitro-
gen interferes. Compare the burning of sulphur in air
with its burning in pure oxygen. Since air contains only
about i of its volume of oxygen, there is about five times
as much oxygen in 1 c.c. of pure oxygen as in 1 c.c. of
air. So the sulphur burning in pure oxygen is supplied, on
the whole, five times as freely with the oxygen to bum it, and,
naturally, it bums more rapidly. On high mountains sub-
stances bum much more languidly than they do at ordinary
levels, because the air is rarefied and the weight of oxygen in
1 c.c. is less.

When a liter of oxygen is mixed with 4 liters of nitrogen
from § 72 (c), the mixture is air in all essential respects. No
heat or light escapes during the mixing. There is no abrupt
change of properties: the properties of the mixture are simply
those of the two gases. In fact the properties of air can be
calculated from those of its two chief elements. In order to
understand this, let us calculate the weight of a liter of air.
1 liter of the nitrogen from § 72 (c) weighs 1.257 grams.

In 100 liters of air there are 79 liters of nitrogen. The
weight of this nitrogen will be:

1.257 X 79 = 99.3 grams
The weight of the oxygen will be:

1.43 X 21 = 30 grams
The total weight of the 100 liters of air will be:

99.3 + 30 = 129.3 grams
And the weight of 1 liter will be:

129 . 3 -i- 100 = 1 . 293 grams,

which agrees with the result obtained by directly weighing
the air in § 69, p. 48.

THE ATMOSPHERE 57

In this way, other properties of air can be calculated. But
a chemical compound is a new substance with its own prop-
erties, and they can only be determined by experiment.

Our results indicate strongly, therefore, that the nitrogen
and oxygen in the air are not chemically combined. But if
air is a mixture the percentage of oxygen in it must vary,
since only compounds have an invariable composition. If
we were to carry out the experiment of § 72 (c) many times
with different samples of air from various places and eleva-
tions, would the loss of volume in passing over the hot copper
always be the same?

The answer is that the method is not accurate enough to
answer the question we have put. The error, even when the
experiment is carefully worked, may be as great as 1%.
There are much more exact ways of analyzing the air, and
these methods have shown that the percentage of oxygen does,
in fact, vary from 20.86 to 20.99. This variation is an abso-
lute and final proof that the air is a mixture. No further
evidence is needed. However, in the next chapter we shall
see that when air dissolves in water it dissolves as a mixture.
Further on in our work it will be shown that, when air is
liquefied, the behavior of the liquid shows clearly that it is
not a compound.

Related Topics

8o. History of Oxygen and the Atmosphere: — Carl Wilhelm
Scheele. — Oxygen was discovered about 1771 by the Swedish
chemist Scheele^ who ob-
tained it by heating mer-
cury oxide and by other
methods. His apparatus
is indicated in Fig. 19,
which is a reproduction
of his own drawing. The
retort containing the
mercuryoxidewasheated
by a charcoal fire, for
the manufacture of gas

dates only from 1812. Pia. 19.— Discovery of oxygen by Scheele.

AN INDUCTIVE CHEMISTRY

When the bladder was distended with oxygen, it was
closed by a string and another bladder tied on in its
place. He called the gas "fire air^' on account of the
violent way in which substances like charcoal and sul-
phur burned in it. He knew that the gas was essential
to the life of animab, and he often called it *' vital air," for
this reason.

Scheele knew that the atmosphere was not all "fire air." By
allowing iron filings to rust in a confined volume of air over water
he removed the oxygen and obtained nitrogen. This he called
"vitiated air" because it did not support combustion or res-
piration.

These and many other great discoveries were contained in
Scheele'sbook, "A Treatise on Air and Fire," which is one of the
classics of our science. His publisher refused to print the book
until 1777, and, in the meantime, both, nitrogen and oxgyen
were independently discovered by British chemists.
8i. Rutherford and Priestley. — In 1772 Daniel Rutherford^

a young Scotch physician, obtained
nitrogen in somewhat the same way as
Scheele had done.

On Aug. 1, 1774, Dr. Joseph Priestley ,
an English clergyman, without knowing
anything of Scheele's work, obtained
oxygen by heating mercury oxide. The
red powder was contained in an inverted
tube containing mercury, and dipping
into more mercury in a dish. The rays
of the sun, f ocussed by a lens, formed the
source of heat (Fig. 20). Priestley was
surprised to find that a candle burned in
the gas better than in air, that mice inhaled it without injury,
and that it could be taken into his own lungs without pain.
82. Antoine Laurent Lavoisier. — Although Scheele had pre-
pared oxygen and determined its properties, yet the part that
it plays in combustion was not clear to h'm. Priestley, also,
had confused ideas on this subject. We have seen that light
in this direction can only be obtained by quantitative work. This
work was done by Lavoisier, who was born in 1743 and was

FiQ. 20. — ^Discovery of oxy-
gen by Priestley.

THE ATMOSPHERE 69

guillotined in Paris, on baseless and absurd charges, during the
Reign of Terror, on May 8, 1794.

Taking his stand upon exact quantitative experiments,
Lavoisier explained the behavior of oxygen in combustion, in
the conversion of metals into oxides, and in respiration, and his
views have guided the progress of our science ever since. Per-
haps the most important part of his work was to place the
balance in the position which it still holds, as the chief tool of the
working chemist.

83. Lord Rayleigh and Sir William Ramsay. — In 1894
Rayleigh undertook to ascertain with the utmost exactness
the weight of a liter of nitrogen. He met with the surprising
difficulty that the weight of a liter of the gas depended upon the
way in which it was made. When the nitrogen was set free from
a nitrogen compound the weight of a liter of it was 1.2505 gram.
The results obtained with the gas from five different nitrogen
compounds agreed closely. But nitrogen obtained from the air,
by the method of § 72 (c), was always heavier: a liter of atmos^
pheric nitrogen weighed 1.2572 gram. This difference was far
greater than the possible error in Rayleigh's work and, to explain
it, he suggested that atmospheric nitrogen was not pure, but
contained a small quantity of some denser gas which had not
yet been separated.

84. Argon. — We have seen (p. 52) that nitrogen combines
with hot magnesium. Rayleigh and Ramsay passed at-
mospheric nitrogen many times through a hot tube containing
magnesium powder. About 1 % by volume remained un-
absorbed, and this was the new gas of which they were in search.
It is colorless, odorless, more soluble in water than is nitrogen
and more easily liquefied. They named it argon, which is from
the Greek and means inert.

85. The Inactive Blements. — The name argon refers to an ex-
traordinary property of the gas. Since the air contains nearly
1 % of argon and since it had never manifested its presence in
any way, it was clear that it must be a very inactive element.
Careful work led to the surprising fact that it was totally in-
active. Rayleigh and Ramsay were unable to get it to enter
into any chemical change, and all subsequent attempts have
failed, like theirs. Compounds of argon are unknovm.

60 AN INDUCTIVE CHEMISTRY

Further work by Ramsay has shown that, in addition to
argon, the air contains slight traces of four other colorless gases
which, like it, are totally inactive chemically. These gases are
Helium, Krypton, Neon and Xenon,

Definitions

Centimeter. One-hundredth of a meter. *

Millimeter, One-thousandth of a meter; one tenth of a centi-
meter.

Sqitare Centimeter. The area of a square whose side is one
centimeter.

Ciibic Centimeter. The volmne of a cube whose side is one
centimeter.

Liter. The volume of a cube whose side is ten centimeters; one
thousand cubic centimeters.

Gram. The weight of a cubic centimeter of water at the tem-
perature at which water is densest (4°). Roughly, this is one-fifth
the weight of a nickel five-cent piece.

Kilogram. One thousand grams; about 2.2 pounds.

Nitride. A compound of nitrogen with another element.

Decompose. To separate a compound into its elements, or into
simpler compounds.

Combustion. Rapid chemical combination attended by the pro-
duction of fight and heat.

Qvmditative. A term applied to experiments in which the
quantities of the substances used, and of the products, are deter-
mined by accurately weighing them.

CHAPTER VI

THE GENERAL PROPERTIES OF GASES.— THE LAWS OF
BOYLE AND CHARLES.— THE KINETIC THEORY

OF MATTER!

86. Solid and Liqtiid. — Iron is always called a solid,
water a liquid and air a gas. Let us consider just what is
meant by this. The most striking distinction is that a
piece of iron has a shape of its own, which it retains; the
air and the water have not. Their shape depends upon that
of the vessel which happens to contain them. To change the
shape of the iron, work is required: the iron opposes a re-
sistance to the change which, within limits, is proportional
to the change in shape enforced upon it.

But is the idea that a liquid has no shape quite exact?
Think of a raindrop. It is not in any containing vessel, and
the fact that it is falling freely removes it from the influence
of the earth's attraction, so far as change of shape is con-
cerned. Raindrops are spherical. By mixing the right
quantities of water and alcohol, one can prepare a liquid
which has the same specific gravity as olive oil (0.92).
If drops of olive oil are placed in this liquid, they float
about freely at any level, and always take the form of spheres.

We may say, then, that a solid has its own shape, which
work is required to change; that very little work is required
to alter the shape of a liquid, which is usually that of the
containing vessel; and that the shape of a liquid freed en-
tirely from any external action, is that of a sphere.

87. Gases. — Let us try, now, to establish some distinc-
tions between the water and the air. We know already that
air is vastly lighter than water. This is a general distinction

' The full treatment of these subjects belongs to Physics. The pres-
ent chapter aims only to give an elementary account of those topics
which are of special importance in the chemical work.

AN INDUCTIVE CHEMISTRY

To Air Pump

Fio. 21. — The expansion of a gas into a vacuum.

between liquids and gases. Since the specific gravities of dif-
ferent liquids are very different and since gases also vary
greatly among themselves in this respect, no definite nu-
merical statement can be made about the matter. If an aver-
age was made of the
'B „.. ? specific gravities of all

liquids and the same was
done with the gases the
relation of one to the
other would probably be
of the order of 1000:1.
If we pour half a liter
of water into a liter
bottle, the water re-
mains in the bottom, and its upper surface is distinct.
All liquids behave in this way but gases never do. Half
a liter of gas admitted into an empty liter bottle, from which
all gas has been removed by an air pump, will
fill the bottle completely.

In the diagram (Fig. 21) the vessels Vi and
V2 have each a capacity of 1 liter. They are
connected by a tube with a stopcock Si. From
V2 another tube with a stopcock S2 leads
to an air pump. Close Si, open S2 and exhaust
V2. Then close S2 and open Si. The liter of
air in Vi at once distributes itself evenly be-
tween the two vessels, and the air pressure in
the apparatus becomes one-half of its value
at the start. If the process is repeated, the same
thing occurs again, and the pressure is reduced Fiq- 22. — The

1 ^ i-t *i • • 1 1 m^ • XX diflfusion of

to one-fourth its original value. Two important gaggg.
distinctions between liquids and gases are,
then, (1) that the density is much higher in the liquids,
the material is more closely packed in them; (2) that
they form an upper surface in a vessel which they only partly
fill, while the gases expand and fill the vessel completely.

THE GENERAL PROPERTIES OF GASES 63

88. Diffusion of Gases. — In Fig. 22 Ci and Ct are two
cylinders of the same size ground to fit air-tight. The upper
cylinder Ci is filled with nitrogen and the lower with oxygen.
Nitrogen is decidedly lighter than oxygen; yet the two gases
mix, and in a Uttle while we find in all parts of both cyUnders
a mixture containing 50% of each gas by volume. Other
pairs of gases act in the same way. Each gas travels into
the other until there is a uniform mixture. This is called
the diffvMon of gases. It means that actual motion of both
gases from one part of the apparatus to another has occurred.
It takes place even when the cylinders are left entirely at rest,
and when change of temperature is excluded.

89. Diffusion in Solids and Liquids. — ^This behavior is not
peculiar to gases. We may use alcohol and water in the two
cyUnders, putting the alcohol in the upper one, because it is
Ughter. The result will be a uniform mixture of the two,
but a longer time will be required than in the case of the two
gases.

When a cylinder of lead is placed with its lower surface
on a disk of gold, gold travels upward into the lead, slowly
in the cold and more rapidly when heated. In the same way
gold will travel into silver and platinum. When the silver
is stripped from an old piece of silver plate it is found that
silver has penetrated into the base metal, and can be de-
tected some distance below the surface.

90. Effect of Pressure upon Solids, Liquids and Gases. —
A cube of iron 10 cm. on the edge has a volume of 1 liter.
Under ordinary circumstances the pressure on it is that of
the atmosphere, which does not depart widely from 760 mm.
of mercury. This means that each square centimeter of
the block is pressed as though it supported the weight of a
column of mercury 1 sq. cm. in cross section and 760 mm.
high. Now imagine the cube placed in a suitable apparatus
and subjected to double this pressure. It would, of course,
be squeezed into a smaller bulk, but the shrinkage would be
very small, so small that it would be difficult to detect. If

64 AN INDUCTIVE CHEMISTRY

we attempted to compress the block till its volume was re-
duced to half a liter, we should find that the pressure re-
quired was beyond the power of any apparatus and that
breakage would put an end to the experiment long before
the result was achieved.

A similar experiment with a liter of water would give about

the same result. Doubling the pressure to two atmospheres-

would scarcely reduce the volume and we should

^^ find that to halve the volume would require the

application of pressures which cannot be handled

with our present appliances. Other solids and

liquids would behave in about the same way as

iron and water. Not in exactly the same way, for

the reduction in bulk caused by doubling the

pressure would be diflFerent for each substance,

but it would be slight in all cases and halving

the volume by pressure would be quite out of

H^j the question.

^^ A liter of air under pressure behaves in

Fig. 23.— ^ ^^^ different and much more simple way.

Boyle 8 Law. *' i

Raising the pressure to two atmospheres
reduces the volume to 500 c.c. If the pressure was
doubled again, the volume would become 250 c.c. If
the pressure was doubled a third time to 8 atmospheres the
space occupied by the air would shrink to 125 c.c. and so on.
The apparatus shown in Fig. 23 affords a simple method of
verifying this law. The air is contained in the short closed
limb of the tube and mercury is poured into the open limb
until the two columns of mercury are of the same height.
The volume of air is then recorded. The pressure is that of
the atmosphere, say 760 mm. If, now, sufficient mercury
is poured into the open limb to cause a difference of level of
760 mm. between the surfaces of the columns of mercury in
the two limbs, it will be found that the volume of
the air is exactly halved. Other gases behave in the
same way.

THE GENERAL PROPERTIES OF GASES 65

We may now sum up the results in a general statement:
At a fixed temperature, the volume of any mass of gas varies
inversely as the pressure upon it. This is called Boyle's LaW|
after the great Irish chemist Robert Boyle, who first stated
it in 1660, Or, we can say that the closeness with which the
matter of the gas is packed is proportional to the pressure;
twice the pressure forces twice the material into 1 c.c. The
closeness of packing, the quantity of a substance in 1 c.c, is
called the concentration. So that we can put the same law
into another form: The concentration of a gas is proportional
to the pressure.

Notice how much simpler the conduct of the gases is than
that of the solids and the liquids. Each soUd and each liquid
behaves in its own way, and there is no simple relation be-
tween pressure and volmne. But all gases behave alike, and
the relation between volume and pressure is of the simplest
sort. The method of using Boyle's law in calculation is ex-
plained in detail in Chap. XXX.

91. Effect of Temperature upon the Volume of a Mass of
Gas. — Returning to our block of iron, let us suppose that its
volume is exactly 1 liter at 0**. If it is warmed to any higher
temperature, it will expand, and its volume will become
greater. This expansion is different at different tempera-
tures, but, on the average, about three hundred-thousandths
of a liter (0.00003 liter) would be added to the volume of
the block for every degree centigrade it was heated. Other
solids would behave in about the same way, but the expan-
sion, though of the same order, would be different in amount
for each. A cube of copper would expand somewhat more
per degree than the iron; a cube of platinum very much
less.

Our liter of water, measured at O*', would contract when
heated until 4** was reached, after which it would expand in a
very irregular way. The expansion becomes greater at high
temperatures. On the average the amount added to the
volmne for each degree rise in temperature would be about

66 AN INDUCTIVE CHEMISTRY

0.0004 liter. We can say, roughly, that the water expands

rather more than ten times as much as the iron.

Each Uquid behaves in its own way. Alcohol expands
more per de^ee than water, mercmy only about half as
much, and more regularly.

If we should measure a liter of air at 0°, and warm it, we
should notice that it expands aboujb ten times as much as the
water and about a hundred times as much as the iron, adding
0.00366 liter — ^that is s^ liter — ^for every degree through
which it is warmed. We should note also that the expansion
is wonderfully regular. A rise of 1° in the neighborhood of
lOO** increases the voliune to exactly the same extent as the
same rise in temperature in the neighborhood of 0°. Finally,
if we tried different gases, nitrogen, argon, oxygen and so on,
we should get the surprising result that the amount of ex-
pansion of each is almost the same. A gas expands ^^ of its
volume at 0** for every degree through which it is heated. This
statement is called Charles' Law.

The law will become clearer, if, instead of starting with a
liter, we think of 273 liters of gas at 0**. Then we should have

at 1** 274 liters

at 2"" 275 Uters

at S*' 276 liters

at 20'' 293 liters

at 100** 373 liters

at 273'' 546 Hters

The law is the same when the gas is cooled. 273 c.c. of
gas at 0** become:

at -1** 272 liters

at -2'' 271 Uters

at -3° 270 liters

at -20° 253 liters

at -100° 173 Uters

at -273**, the absolute zero of Physics, if the gas continued
to contract regularly, the volmne would become zero and
the gas would disappear. This, of course, is absurd, and it
means simply that we have applied the law at temperatures

THE GENERAL PROPERTIES OF GASES 67

at which it no longer holds good. Temperatures around
-272° have actually been obtained. At such temperatures
all gases except helium become solid, and the law of contrac-
tion loses its meaning.

So far, then, as the efifect of heat goes, gases differ from
solids and liquids in three important respects:

L They expand very much more for equal increase in tem-
perature.

2, The expansion is almost perfectly regular.

3. The expansion is almost the same for all gases.

The method of applying Charles' Law in practical calcula-
tion is explained in Chap. XXX.

92. The Kinetic Theory. — The behavior of gases with re-
spect to temperature, their behavior under pressure and their
diffusion (§88) make up a remarkable group of properties.
In 1738 Daniel Bernoulli constructed an hypothesis which ex-
plains these properties so perfectly and which is so strongly
supported by very recent research that it has ceased to be an
hypothesis and has become a fact. Since there is hardly any
doubt that it gives a picture of the actual structure of gases
— ^and, to some extent of solids and liquids — and since it has
important applications to chemical work, it must be thor-
oughly imderstood.

A Uter of oxygen, measured under ordinary pressure,
can be squeezed by increased pressure into a volume of about
1 c.c. There are two ways, and only two, of looking at this
fact: (1) The actual matter of the gas is compressed until it
occupies only about roVrr of the original space; (2) the gas did
not really fill the volume of 1 liter in the first place, because it
is composed of particles with large spaces between them;
under pressure, the particles are pushed more closely to-
gether, the matter becomes more densely packed.

The kinetic theory of Bernoulli starts from the second
idea. A gas is composed of particles which are separated by
spaces very large in proportion to the size of the particles.
How, then, are we to explain the fact that a mass of gas com-

68 AN INDUCTIVE CHEMISTRY

pletely fills any vessel in which it is placed ? At first thought,
we should expect a liter of oxygen to settle until the particles
were in contact, forming a thin layer upon the bottom of the
vessel and leaving the space above empty.

There is an easy answer to this question. The particles
are not at rest, but in rapid, continual motion in straight
lines. Each moves until it strikes another, or the wall of the
vessel, when it rebounds in some new direction. Imagine a
lot of billiard balls, rolling about and continually rebounding
from each other and the rim of the table. Imagine also that
the balls are perfectly elastic, so that no motion is lost during
a rebound, and the movement will keep up forever. Finally
imagine that the motion takes place in three dimensions in-
stead of in two. Or, think of a swarm of angry, tireless
bees, shut up in a box.

93. The Molecules. — We shall call these particles mole-
cules. The average speed of a molecule of oxygen is about
that of a rifle bullet, say half a kilometer per second. In our
illustration of the billiard balls, it is plain that there would be
continual violent blows against the rim of the table. Now if
the balls were very numerous, these blows would be delivered
so frequently that they would no longer be perceived
separately. Instead of a series of shocks they would
produce the efifect of a steady pressiu'e. The pressure of
a gas is the bombardment of the molecules against the
surface pressed.

If a liter of oxygen is squeezed into half a liter there must
be twice as many molecules in each cubic centimeter of the
gas as before. Hence twice as many molecular blows will
be delivered per second against every square centimeter of
the surface in contact with the gas — ^the pressure will be
doubled. For the same reason, if the gas is squeezed into
one-fourth of a liter, the pressure will be four times as great
9S at the start, and so on. This is Boyle's Law,

94. Diffusion. — Diffusion (§88) is a direct result of the
movement of the molecules. The forward movement of the

THE GENERAL PROPERTIES OF GASES 69

molecules of oxygen carries them up into the nitrogen, while
the molecules of nitrogen move downward. Other pairs of
gases act similarly. Returning to our billiard-ball illustra-
tion, if we imagine that, at the start, the balls on one-half of
the table were all red and those on the other half all white, it
is plain that in a little while they would be imiformly mixed.
Or, using the other simile, if we imagine that, at the beginning
of the experiment, the upper half of the box was occupied by
wasps and the lower half by bees, we see at once, that after a
short time, the aimless flyhxg of the insects would mix them
uniformly.

The diffusion of alcohol in water (§89) proves that the
molecules of liquids must also be in motion. The chief
difference is that, in the liquid, the molecules are much more
closely packed than in the gas, and the average distance a
molecule moves before colliding with another is much shorter.
The diffusion of metals into each other (§89) shows that the
molecules of soUds are in motion. But, on account of the
great cohesion of solids, a molecule does not easily leave its
place and move forward to a new position.

95. Visible Proof of the Motion of Molecules. — We have
looked into this matter far enough to see that the theory of
molecules in motion explains the behavior of gases in a very
simple and satisfactory way. To proceed further requires
the aid of the higher mathematics. The subject has been in-
vestigated fully by Maxwell, Boltzmann and others, who have
shown that the agreement between the theory and the facts is
nearly perfect. But even this does not show that the theory
is true, for some other idea might be imagined which would
explain the facts equally well.

Suppose, for illustration, that we were watchmg the motion

of the hands of a clock. To account for this motion we might

construct an hypothesis that the 'hands were moved by a

spring which had been wound up. This would explain the

motion perfectly, and yet it might turn out, after all, that the

clock was run by a weight.
6

70 AN INDUCTIVE CHEMISTRY

In order to be sure we want to see the motion of the mole-
cules. This looks hopeless on account of their inconceivable
smallness. Calculations based on the very theory we are
now studying show that in a Hter of air — or any other gas —
under 760 mm. pressure and at 0°, the number of molecules
is 3 X 10^, that is, 3 followed by 22 ciphers. In order to
get some idea of the magnitude of this number, suppose that
we have a liter of air confined in a bottle, with a hole from
which a million molecules escape every second, while nothing
enters. Nearly a thousand million years would elapse before
all the molecules had left the bottle.

However, we have seen that it is difficult to set Umits to
the progress of our science, and the task of making the mo-
lecular motion visible has recently been accompUshed. In
order to understand how this was done, let us start by think-
mg of a mote, floating in a sunbeam m still air. Accordmg to
our theory the mote is being battered on all sides every
second by countless millions of molecules moving with about
the speed of rifle bullets. It remains at rest because it is very
large and heavy in proportion to the molecules and the blows
in opposite directions neutralize each other. Now imagine
the mote to grow smaller until it is not very much larger or
heavier than the molecules themselves. The number of
molecules striking it each second will decrease, and the mo-
tion given it by the blows will increase. There must come a
time when a molecule striking it, say on the right, will give
it a perceptible push toward the left before another molecule
will collide with it and send it back.

Recently chemists have succeeded in obtaining, floating in
air, a dust of silver so fine that each grain can contain only a few
molecules. When viewed under a powerful beam of electric
light, with a good microscope the silver particles are seen to be
darting about in a zig-zag path composed of straight lines. The
motion is exactly that which our theory supposes, and it goes
on without interruption or slacking up for an unlimited time.
Very small particles of gold (and other metals) suspended in

THE GENERAL PROPERTIES OF GASES 71

water, h^ve the same ceaseless zig-zag motion, due to the colli-
sion of the moving water molecules with the particles of gold.
96. Solutions of Gases in Water. — Fig. 24 represents a

glass tube which has been filled with pure, cold boiled water

and inverted in a dish containing the

same liquid. The object of the boiling is

to drive out the gases which water always

takes up from the air. A little nitrogen is

passed up into the tube.
What does the kinetic theory predict?

The surface of the water will be battered

by a hailstorm of nitrogen molecules.
Some of them will penetrate
the siu^ace and move about
among the water molecules.
That is, some of the gas will
dissolve in the water. But, as
the number of nitrogen mole-
cules in the liquid grows larger,
more and more of them will
break through the surface of the liquid upward
and return to the portion of the tube occupied
by the gas. When the number passing upward
through the surface per second is equal to the
number passing downward, no more nitrogen
will dissolve. The water will be saturated with
it. There is no reason to think that a sudden
stagnation, a stoppage of everything, has oc-

FiQ. 24.— Solubility
of gases.

„ , curred. The molecular storm continues, but its

Fia. 25. — Solu-

buityofnitro- cffccts in the t WO directious balance. Equilibrium
gen(quantita- betwccu them has been reached. Using our equa-
tion method we may write this equilibrium thus:

Nitrogen (gas)

Nitrogen (dissolved).

This means simply that, in each second, just as much m-
trogen dissolves in the water as is liberated from it.

72 AN INDUCTIVE CHEMISTRY

Quantitative information about the solubility of. nitrogen
can be obtained by the apparatus shown in Fig. 25, which is
a graduated tube closed by a stopper. Through the hole in
the stopper passes a glass tube ending in a rubber tube bear-
ing a clamp. The graduated tube is filled with pure water,
free from air. It is clamped with the open end dipping
into boiled water and a little nitrogen passed in through a
rubber tube which reaches to the top. The voliune of the
nitrogen is read and that of the water remaining in the tube
is obtained by subtraction.

The next step is to insert the stopper, close the clamp and
shake vigorously. Then the clamp is opened under water
and, of course, the voliune of water which enters is a measure
of the amount of nitrogen which has been dissolved.

In this way it is found that water dissolves very little ni-
trogen, and less at high temperatures than at low.

100 c.c. water dissolves at 0° (freezing-point) 2 c.c.

100 c.c. water dissolves at 20° (room temperature) 1.5 c.c.
100 c.c. water dissolves at 80° 0.5 c.c.

1(X) c.c. water dissolves at 1(X)° (boiling-point) a volume too

small to detennine

All other gases are more soluble in water than nitrogen.
Oxygen is very slightly soluble, yet it dissolves about twice
as freely as nitrogen.

100 c.c. water dissolves at 0® 4 c.c. oxygen
100 c.c. water dissolves at 20° 3 c.c. oxygen

97. Effect of Pressure on the Solubility of Gases. — So

far, we have supposed the nitrogen to exist at the pressure
of one atmosphere. What would be the effect of doubling
the pressure? The kinetic theory returns a straightforward
answer to this question. Doubling the pressure will crowd
twice as many molecules of nitrogen into each cubic centi-
meter of the gas and twice as many will strike the surface of
the liquid per second. Since the amount of nitrogen taken
up by the water depends upon the frequency of the molecular
blows, twice as much gas should dissolve. Experiment con-

BOBERT WILHELM BUNSEN
B. Germaay. 1811. D. 1886.

THE GENERAL PROPERTIES OP GASES 73

firms this prediction. A double pressure forces a
double quantity of gas into the water. In general terms,
the solvbility of a gas is proportional to the pressure of
the gas upon the surface of the liquid. This is called
Henry's Law.

98. Solubility of Air in Water. — ^To prove that air dis-
solves in water, we need only fill a glass from the hot-water
faucet in the kitchen. The small air bubbles which separate
make the water milky. In a moment they escape and the
liquid is clear. The abundance of animal life in water shows
that oxygen must dissolve in it. If a globe of goldfish is
put under an air pump, so that the dissolved air is taken out
of the water, the fish suffocate.

We must now ask another question of the kinetic theory.
In what proportions will the nitrogen and oxygen of the air
dissolve in water ? Will the dissolved air have the same com-
position as ordinary air, that is, about four-fifths nitrogen to
one-fifth oxygen by volume?

First of all, there is no reason to think that the presence of
either gas will affect the behavior of the other. We can work
out the problem for each gas as though the other were not
present.

Since air contains one-fifth of its volume of oxygen, oxygen
molecules will strike the surface of the water one-fifth as fre-
quently as if the water was in contact with pure oxygen.
100 c.c. water dissolves, in contact with pure oxygen, 4 c.c.
of the gas. In contact with air, it ought to dissolve i of 4
c.c, or 0.8 c.c. of oxygen.

For the same reason, the amount of nitrogen dissolved from
air ought to be 4 of the volmn^ dissolved when the water is
in contact with pure nitrogen. This gives (§96), 2 X J
= 1.6 c.c, for 100 c.c. water. Bunsen foimd, by direct ex-
periment, that 100 c.c. water dissolved from air 2.47
c.c. of gas, of which 1.61 c.c. was nitrogen and 0.86
c.c. oxygen. The agreement between theory and fact
is close.

74 AN INDUCTIVE CHEMISTS^Y

This is another proof that the air is a mixture. For the
calculation we just made is based upon the idea that the ni-
trogen and oxygen are separate in it. If the air were a com-
pound, it would dissolve unaltered in water and the composi-
tion of the dissolved air would be the same as that of the
original atmosphere.

99. Avogadro's Hypothesis. — ^The most striking fact about
gases is that they all behave in about the same way when
pressure or temperature is changed. Each solid and each
liquid behaves in its own way. The only reasonable conclu-
sion from this is that, in some respect, the structure of all
gases must he alike. This likeness cannot be in the molecules
themselves, for they are composed of different substances,
and have, as we shall see, different weights in different gases.
The similarity, then, must be in the closeness of packing, in
the spacing of the molecules. The average distances between
the centers of the molecules in oxygen and nitrogen, for in-
stance, must be the same when the two gases are at the same
temperature and pressure. And the molecules in the two
gases must approach each other to the same extent for an
equal increase of pressure, and must separate to the same ex-
tent for an equal increase of temperature, so that the spacing
always remains the same, so long as the two gases are at the
same temperature and pressure. The same remark applies
to all other gases.

Now if the spacing or closeness of packing of the molecules
is the same in all gases, imder the same conditions, then, at
equal temperature and pressure, one liter of all gases must
contain the same number of molecules. This statement
is called Avogadro's H3rpothesis, after Amadeo Avogadro,
who proposed it in 1811. We may put it thus:

Equal volumes of all gaseSj measured at the same
temperature and pressure^ contain equal numbers of
molecules.

Calculation shows that for a liter of gas at 0° and 760
mm. the number of molecules must be about 3 X 10^, but

THE GENERAL PROPERTIES OF GASES 75

in chemistry we are concerned only with its equality in
different gases, not with the number itself.

100. All the Molecules of the Same Gas Must be Exactly
Alike. — Every molecule of oxygen must be exactly like every
other, and must have the same weight. For if oxygen con-
tained molecules which differed in size and weight, it would
be possible to separate it, by some process of the nature of
sifting, into two portions, one of which would contain lighter
molecules and be less dense than the other; and other gases
could be separated into different specimens in the same way.
Elaborate and painstaking attempts have been made to
separate various gases into two portions of different densities,
and they have always failed.

Definitions

Solid. A body which has a shape, which it retains, imless dis-
torted by external force.

Ldquid, A body which takes the shape of the containing vessel,
and has a limiting upper surface.

Gas, A body which takes both the shape and the volume of the
containing vessel. A gas has no upper surface because it completely
fiUs any vessel in which it is contained.

Density, The quotient obtained by dividing the weight of a
body by its volume; the weight of unit of volume.

Molecule, The small particle of a gas which moves about as a
whole, during the heat motion of the gas.

Kinetic theory. The theory which explains the properties of
gases by the fact that heai is molecular motion, so that, at all
temperatures above the absolute zero, the molecules are in ceaseless
movement.

BOOK II

COMPOUNDS OF OXYGEN

INTRODUCTION

In spite of its importance, the quantity of oxygen in the
air is small compared with that which exists in oxygen com-
pounds. We shall see that water contains eight-ninths of its
weight of oxygen* If the earth's surface was perfectly even
(a geometrical sphere) the water would cover it everywhere
to a depth of about 300,000 cm. (nearly two miles). A layer
of water only 264 cm. (8| ft.) deep would contain as much
oxygen as the atmosphere. Therefore the water on the
earth's surface contains more than 1000 times as much
oxygen as the atmosphere.

But the quantity of oxygen in the water is trifling compared
with the enormous mass which exists, in chemical combina-
tion, in the rocks. Calculations based on thousands of
analyses show that, on the whole, the materials of which the
accessible portion of our planet consists contain about half
their weight (49.78%) of oxygen. Oxygen is, therefore
by far the most abundant of the elements.

We shall first study, in Chap. VII, the compounds which
oxygen forms with the metals we have already taken up.
Following the same plan. Chap. VIII will be devoted to the
oxides of the non-metallic elements sulphur and carbon.
This will lead naturally in Chaps. IX and X to the study of
some minerals which are oxides of elements not yet familiar
to us. The concluding chapter of the book will contain an
explanation of the method of converting sulphides into oxides
by heated air, and oxides into metals by heated carbon.
These processes are important in the extraction of metals
from their ores.

CHAPTER VII
OXIDES OF FAMILIAR METALS

101. Lead Monoxide. — Melted lead absorbs oxygen and
becomes covered with a yellow film of lead monoxide. Com-
plete conversion is achieved by steady heating in a furnace
where a current of air is drawn over the surface of the liquid
metal.

Lead monoxide appears in commerce in two forms.
Litharge is a mass of yellow-red crystalline scales, used in the
making of lead glass. Massicot is a dull yellow powder, used
in making other lead compounds, especially red lead. Both
forms are nearly insoluble in water. They turn dark brown
when gently heated, and melt readily. They have the same
composition, containing for one part of lead, 0.0773 part of
oxygen. This could be investigated by weighing out a gram
of lead in a porcelain crucible, converting it into lead mon-
oxide and weighing again. The better the balance, and the
more careful the work, the more nearly would the weight of
the lead monoxide approach 1.0773 gram.

102. Red Lead or "Minium". — When massicot is per-
sistently heated to a very low red heat (500**) in a current of
air, it passes into a bright scarlet powder, red lead. That
oxygen is taken up is indicated by the fact that the weight
increases. Proof can be obtained by heating the red lead
to a higher temperature in a glass tube, when it is again con-
verted into massicot. Oxygen escapes, and can be collected
over water and identified by thrusting into it a glowing splint.

Red lead is an oxide of lead which contains more oxygen
than lead monoxide. We have seen that the equation

«^-sulphur < ^ /^-sulphur

proceeds from left to right at 100° and from right to left at

OXIDES OF FAMILIAR METALS 79

room temperature. This is a similar case. The equation
Lead monoxide + oxygen < ^ red lead

proceeds in air from left to right below 550*" and from right
to left above that point. Red lead, mixed with linseed oil,
is much used for painting iron and steel, to protect them
against rust.

103. Lead Dioxide. — Lead dioxide is a dark brown powder
used in storage batteries and in making matches. It is made
by treating red lead with nitric acid. Heated in a glass tube,
it behaves Uke red lead; oxygen escapes and lead monoxide
is left. The weight of this oxygen can be easily foimd by
gently heating a weighed quantity of lead dioxide in a por-
celain crucible. Let us weigh off 1.1546 grams in an un-
covered crucible, weighing with it a short glass rod for
stirring. Heat gently and stir until the powder has turned
completely to yellow lead monoxide. The weight is now
1.0773 grams, .0773 gram of oxygen has escaped.

We have proved, then, that there are:

1 gram of lead + .0773 gram oxygen in lead monoxide.

1 gram of lead + 2 X .0773 gram of oxygen in lead dioxide.

Hence the prefixes mon- and di-. They are from the Greek
, numerals for one and two.

104. Iron Monosulphide and Pyrite. — Multiple Propor-
tions. — The law that emerges from these numbers is one of
the foundations of our science. Before we put it into words,
let us make sure we understand it by calculating another
example.

There are two compounds of iron and sulphur. One of them, pyrite,
we already know. Its chemical name is iron disulphide. The other,
tr<m monosidphide, is one of the stock-materials of every laboratory.
It is made by heating a mixture of iron and sulphur to redness. In
order to find out its composition, let us weigh out a gram of pure iron
powder in an uncovered porcelain crucible, add about a gram of sul-
phur, cover the crucible, and heat until sulphur no longer escapes be-
tween crucible and lid. Then we weigh again, without the cover.

80 AN INDUCTIVE CHEMISTRY

The substance is pure iron monosulphide, for the sulphur which did
not combine with the iron is vaporized.

The weight of the iron monosulphide is 1.5714 grams.

We know that pyrite loses part of its sulphur when heated. Let us
weigh 2.1428 grams of powdered pyrite in an uncovered crucible,
cover and heat intensely until no more sulphur escapes, cool, and weigh
without the cover. Iron monosulphide remains, and its weight is
1 .5714 grams. The sulphur driven off is 0.5714 gram.
1 gram of iron is combined with 0.5714 gram sulphur in iron mono-
sulphide.
1 gram of iron is combined with 2 X 0.5714 gram sulphur in iron
disulphide.

Now we can state the law in a general way. Suppose that
two elements A and B form two compomids with eack other.
Let us consider any fixed weight of A. Then the quantities
of B, which are combined with this fixed weight of A in the
two compounds, will bear some simple relation to each other.

Thus, if we take any fixed weight of iron, the sulphur
in iron monosulphide bears to the sulphur in iron disulphide
the relation of 1 : 2. If we take any fixed weight of lead, the
oxygen in lead monoxide bears to the oxygen in lead dioxide
the relation 1 : 2. The relation is not always 1 : 2. It may be
1 : 3, 2 : 3, etc., but it can always be expressed by small
whole numbers. Thus, if we determine the quantity of
oxygen imited with one gram of lead in lead monoxide, and
also in red lead, we find that the two weights bear the rela-
tion 3:4.

This general statement is called the law of multiple pro-
portions. The name is a poor one, because the proportions
are not always multiple. The essential thing is that they
bear to each other a relation which can be expressed by small
whole numbers.

105. Zinc Oxide. — Only one compound of oxygen with
zinc has been obtained. It is called zinc oxide and can be
made by burning zinc in the air. It is a loose white powder,
insoluble in water. It is lemon yellow while hot. Mixed
with linseed oil, it is much used as a paint under the name

OXIDES OF FAMILIAR METAI5 81

"zinc white." It is not poisonous. Since artificial zinc sul-
phide is white, zinc oxide paint is not discolored by gases con-
taining sulphur. Zinc oxide is largely employed as a "filler"
to mix with the rubber from which automobile tires are made.

io6. Compounds of Mercury with Oxygen. — ^When mer-
cury is allowed to stand exposed to air, small quantities of a
black powder called mercurous oxide are formed on the sur-
face. It contains 4 grams of oxygen combined with each
100 grams of mercury.

Mercuric oxide contains 8 grams of oxygen for each 100
grams of mercury. Notice the multiple proportion. Notice
also the meaning of the terminations ous and ic. When there
are two oxides of the same element, the termination ous is
often given to the one which contains the sm^lest percent-
age of oxygen and ic to the one which contains the greatest

Mercuric oxide is a brick red powder, which turns black
when gently heated and recovers its red color on cooling. At
the temperature of liquid air (-192°) it has the color of sul-
phur. We have noted its historical interest and studied its
decomposition by heat. We have seen also that mercury,
heated close to its boiling-point in air, slowly passes into mer-
curic oxide. This is too slow to serve as a method of prep-
aration. The oxide is made more quickly by treatmg mer-
cury with nitric acid and heating the resulting substance to a
temperature short of a red heat. Mercuric oxide is slightly
soluble in water and, like most mercury compounds, is poison-
ous. It is used m medicine in ointments for external use.

107. Oxides of Copper. — ^When sheet copper is heated in
air two oxides are formed. Next the copper is a red layer of
cuprous oxide, and on the outside a black layer of cupric
oxide. This indicates that cupric oxide is richer in oxygen,
since it is formed where the oxygen is more abundant. In
fact analysis shows that with 100 parts of copper there are
combined

in cuprous oxide 12.6 parts of oxygen
in cupric oxide 25.2 parts of oxygen.

82 AN INDUCTIVE CHEMISTRY

This is another instance of multiple proportions. The law
still holds good if we calculate the weights of copper united
with a fixed weight of oxygen in the two compounds. Thus,
for 100 parts of oxygen, there are

in cupric oxide 396.9 parts of copper
in cuprous oxide 793.8 parts of copper

and these numbers are to each other as 1 : 2.

Cuyrous oxide is a red powder. It is found crystallized
in octahedra as the mineral cuprite, Cupric oxide is black.
It is unaltered by ordinary heating, but at the temperature

of the electric furnace it separates into
oxygen and copper. It has important
uses in the laboratory.

io8. Oxides of Iron. — ^The mineral
magnetite crystalUzes in octahedra
which are iron-black and yield a black
Fig. 26.— A rhombohedrai powder, strougly attracted by the

magnet. Some specimens are naturally
magnetic (lodestone). When pure, it contains 72.40%
of iron and 27.60% of oxygen. It is one of the im-
portant ores of iron. Great beds of it are found in the
Adirondack region, in northern New York, and in the
famous iron mines of Sweden.

Hematite crystallizes in rhombohedrons (Fig. 26) which
have a dark steel-gray color not unlike that of magnetite, but
the powder is bright red and is not picked up by a magnet.
It is the most important iron ore and is found in enormous de-
posits in northern Minnesota, Michigan and Wisconsin.
About fifty million tons of hematite are mined each year in
this region.

When pure, hematite contains 70% of iron and 30% of
oxygen. Its chemical name is ferric oxide (from the Latin
ferrum, iron). Large quantities of ferric oxide are made
artificially. It is used as a polishing powder for glass and
metals and as a cheap paint for freight cars, roofs, bams

OXIDES OF FAMILIAR METALS 83

and fences. The red color of bricks and earthenware is due
to small quantities of ferric oxide.

The oxide formed when iron bums in oxygen has the same
composition as magnetite. The black scales that fall from
iron under the blacksmith's hammer resemble magnetite,
but they seem to contain some unbumt iron mixed with the
oxide, for their composition varies.

Limonite is also an important iron ore. It is found not in crys-
tals, but in masses which are black and lustrous on the surface,
but brown in the interior. It is f oimd in Connecticut and New
York near the boundary of the two states, in Pennsylvania
and elsewhere in the eastern U. S. It is used as a brown paint.

When dry limonite is heated in a dry test tube, water ap-
pears in the upper part of the tube and ferric oxide is left.
The proportions of water and ferric oxide from pure limonite
are always the same. It follows that limonite is a compound
of ferric oxide and water. Like elements, compounds may
unite to form more complex compounds in which their
properties are completely lost.

109. Oxides of the Precious Metals, Goldi Platinum and
Silver. — Since the precious metals are not acted upon by air,
even at a red heat, it is clear that their oxides are not easily
formed by direct combination. On the contrary the oxides
separate easily into oxygen and metal at a gentle heat or even
in the cold, under the influence of light. The oxides of
gold and platinum are black or brown powders, which lose
their oxygen so readily that they are difficult to prepare.

no. Silver Oxide. — When silver powder is heated to 300® in pure
oxygen at a pressure of 20 atmospheres (20 X 760 mm.) the two ele-
ments combine to form silver oxide. This is a brown powder, which
can be more easily made by other methods. In air the pressure of
the oxygen is 760 mm. X i or about 150 mm. Now in air at 300®
gilver oxide loses its oxygen completely , leaving a Ittstrous mossy residue of
silver. It appears, therefore, that the change

Silver + oxygen Ii^_ silver oxide
can be made to travel either forward or backward, at the same tem-

84 AN INDUCTIVE CHEMISTRY

peratiire, by simply altering the closeness of packing (concentration)
of the oxygen. When the concentration of the oxygen is high it unites
with the silver; when it is low, the silver oxide separates.

This influence of the concentration of the reacting substances upon
the progress of a chemical change is one of the most important things
we have to understand. First, let us get a clear idea of what concentra-
tion means. It is the closeness with which a substance is packed — the
quantity of it in 1 c.c. of the space in which the chemical change takes
place. In the above example the concentration of the oxygen is stated
in terms of pressure, because, according to Boyle's law, concentration
in gases is proportional to pressure and is measured by it (p. 65). In
pure oxygen, at 20 atmospheres, the pressure of the oxygen is just about
100 times as great as it is in air at 1 atmosphere. But the essential
thing is not that the pressure of the oxygen is 100 times as great, but
that 100 times the oxygen is crowded into 1 c.c. This means that
100 times as much oxygen is offered to the silver by the gas in con-
tact with it. Naturally, this favors the production of silver oxide.

We have shown that, in pure oxygen^ combustions are much more
energetic than in air. The reason is simply that, in pure oxygen, the
concentration of the oxygen is five times as great.

III. Percentage Composition of Important Oxides and
Stilphides. — ^The following tables give the percentage com-
position of some important oxides and sulphides. Only one
of the substances is new to us. This is ciipric sulphide. The
compound of copper and sulphur which we have made and
studied is called cuprous sulphide. Cupric sulphide con-
tains twice as much sulphur, combined with the same weight
of copper. It is a dark blue mineral found on lava at
Vesuvius, in Chili and elsewhere.

SuLPmDES OxmES

1. Lead sulphide 2. Lead monoxide

r 13.39% sulphur f 7.18% oxygen

186.61% lead 192.82% lead

3. Mercmc sulphide 4. Mercmc oxide

r 13.79% sulphur f 7.41% oxygen

I 86 . 21 % mercury \ 92 . 59% mercury

5. Zinc sulphide 6. Zinc oxide

r 32 . 82% sulphur f 19 . 63% oxygen

I 67 . 18% zinc 1 80 . 37% zinc

OXIDES OF FAMILIAR METALS 86

Sttlfhides Oxides

7. Cupric sulphide 8. Cupric oxide

r33.61% sulphur 120.13% oxygen

166.49% copper 179.87% copper

9. Cuprous sulphide 10. Cuprous oxide

r 20. 13% sulphur ( 11 . 19% oxygen

179.87% copper 188.81% copper

11. Silver sulphide 12. Silver oxide

r 12.90% sulphur ' ( 6.90% oxygen

187.10% silver 193.10% silver

13. Iron monosulphide 14. Magnetite

r 36.36% sulphur f 27.59% oxygen

163.64% iron 1 72.41% iron

16. Iron disulphide 16. Ferric oxide

r 53.33% sulphur f 30.00% oxygen

146.67% iron 170.00% iron

X 112. Discussion of the Table. — This table contains a mass
of information, but it is in a form in which it could not be used
with comfort and could not be remembered at all. Looking
through the column of oxides, we fail to discover any relation
between the numbers expressing the quantities of oxygen in
them. There is the same absence of connection between the
quantities of sulphur in the eight sulphides given in the table.
Now let us take the first plain step in the direction of
simplifymg matters. Let us choose some fixed quantity of
oxygen and calculate the quantity of the metals combined
with it in the oxides. The standard quantity of oxygen,
chosen by the chemists of the world, is i6 grams. The rea-
sons for the choice of the number 16 will appear later. The
calculation is made by proportion.

For lead monoxide (2) 7.18 : 92.82 :: 16 : aj .*. x = 207

For mercuric oxide (4) 7.41 : 92.59 :: 16 : aj .*. aj = 200

For zinc oxide (6) 19.63 : 80.37 :: 16 : aj .'. x = 65.5

For cupric oxide (8) 20.13 : 79.87 :: 16 : a; .'. z = 63.5

113. Calculations Based upon the Table. — This device rids
us of half the numbers in the table of oxides, for if the
quantity of oxygen is the same in all, we have only to remem-

86 AN INDUCTIVE CHEMISTRY

ber the quantity of metal. We might re-calculate the com-
position of the sulphides in a similar way, by choosing some
fixed weight of sulphur and so simplify the sulphide table.

But need the choice of the standard weight of sulphur be
arbitrary? Are we, in fact, free to choose it at all ? Does it
not follow from the choice we have already made, of 16 grams
of oxygen as a basis? Sixteen grams of oxygen combine in
lead monoxide with 207 grams of lead. What quantity of
sulphur combines with 207 grams of lead?

This question is answered at once by a proportion based on
the figures given in (1).

86.61 : 13.39 :: 207 : a; .\ a; = 32

This quantity of 32 grams of sulphur is related in a very
real way to the standard quantity of 16 grams of oxygen —
they both combine with the same weight of lead. So far as lead
is concerned 32 grams of sulphur will take the place of, or are
equivalent to, 16 grams of oxygen.

Therefore we have a good reason for using 32 grams of sul-
phur as a basis for our re-calculation of the table of sulphides.
How much mercury will combine with 32 grams of sulphur?
From (3) we construct the proportion

13.79 : 86.21 :: 32 : a; .*. a; = 200.

This surprising result is. of the greatest importance. The
same 200 grams of mercury which combine with the standard
quantity of oxygen (16 grams) also combine with the stan-
dard quantity of sulphur (32 grams).

From (5) we calculate the quantity of zinc which combines
with 32 grams of sulphur

32.82 : 67.18 :: 32 : a; .*. a; = 65.5
This is the same weight of zinc which we found in zinc oxide,
combined with 16 grams of oxygen.

For copper, we have from (7)

33.51 : 66.49 :: 32 : a; . ' . x = 63.5
Again we get the same quantity which combined with 16
grams of oxygen.

OXIDES OF FAMILIAR METALS 87

So far as the compounds from (1) to (8) inclusive are con-
cerned the following holds good: that we have assigned a
number to each element, and that we can write the composi-
tion of any one of the eight compounds by simply setting
down the numbers corresponding to the elements it contains.

114. The Composition of Chemical Compounds. — Recalling
the fact of multiple proportions (p. 80) we may conjecture
that it will often be necessary to mvMiply these standard
quantities by small whole numbers in order to write the com-
position correctly. Foij instance, cuprous oxide contains
twice as much copper, for the same weight of oxygen, as
cupric oxide (p. 85). If cupric oxide contains one standard
quantity each of oxygen and copper, then cuprous oxide must
contain one standard weight of oxygen combined with two
standard weights of copper. In fact by proportion we ob-
tain from (10):

11.19 : 88.81 :: 16 : a; . • . a: = 127 grams

for the weight of copper combined with 16 grams of oxygen
in cuprous oxide. 127 is 63 . 5 X 2 or twice the standard
quantity of copper.

For the quantity of copper combined with 32 grams of
sulphur in cuprous sulphide we get from (9):

20.13 : 79.87 :: 32 : x / , x = 127 or 63.5 X 2.

So that cuprous sulphide contains two standard quantities
(63.5 grams X 2) of copper combined with one standard
quantity (32 grams) of sulphur.

There are about 60 metals and we might have included
them all in our table. The amount of calculation would
have been greater, but the results would have been similar.
We would have obtained a number for each metal, and by
means of these numbers the composition of the oxides and sul-
phides of the metals could have been written.

Fifteen non-metallic elements are known and if we had
included them with all of the metals, our table would have
covered the whole field of chemical science, with the ex-

88 AN INDUCTIVE CHEMISTRY

ception of the elements of the argon group (p. 59), which
form no compounds. We should have obtained for each
element a figure which, multiplied when necessary by small
whole numbers, would express the quantity in which it
entered into all its compounds, provided that the quantities
of the other elements were also expressed by the nimibers
which we had assigned to them.

Such a complete system of numbers is given in the table
on the inside of the back cover. The numbers are called
atomic weights for reasons we sl^all discuss later. The
meaning of the table is that the composition of every chemical
compound can be expressed by the numbers in it, multiplied
where necessary. Thus, suppose that a new compound is
prepared, which is proved to contain nothing but nitro-
gen and sulphur. We know beforehand that the quantity
'of nitrogen in it must be 14 X a; and the quantity of sulphur
32 X y where x and y are small whole numbers, not often as
great as five. So the problem of expressing its composition
becomes the simple one of finding what small multiples of
the standard weights are required.

115. Sjrmbols and Formulas. — The symbols given in the
table indicate the atomic weights of the elements. Thus S
means not merely sulphur, but a special quantity of sulphur,
32 grams. In the same way O indicates 16 grams of oxygen
and Zn 65.5 grams of zinc. We should avoid using these
symbols as though they were merely abbreviations of the
names, and learn to connect with them the idea of a definite
quantity by weight, different for each substance.

The numbers should not be memorized. They will grow
familiar by use. The values given in the column headed
''approximate" are to be used in solving all problems. Those
elements which are important enough to be studied in detail
are in italics in the tables. The others are rare and will be
considered briefly or not at all.

Remember, however, that from the standpoint of pure science —
which is, in the long run, the only truly practical standpoint — ^a rare

OXIDES OP FAMILIAR METALS 89

element is a distinct fonn of matter, and is just as interesting to the
chemist as a common one. Also the mere fact that an element is not
abundant does not mean that it is useless. Great progress has been
made of late in the utilization of the rare elements, and substances
like thorium, cerium, timgsten and tantalum are the raw materials of
great industries. The scientific curiosity of one decade is the necessity
of the next.

ii6. Uses of the Symbols. — The symbol is the first
letter of the name of the element. A second letter is added
where confusion with some other symbol would result if
only one letter was used. Thus, for silicon Si is used, because
S is already taken for sulphur. The symbols are the same in
all languages. In some cases it happens, especially with famil-
iar metals, that the name begins with different letters in dif-
ferent languages. In order to preserve the international
character of the system, the symbol is then made from
the Latin name. A reference to the table will show
that this has been done with iron, gold, lead and other
metals.

In expressing the composition of compounds, the symbols
of the elements are placed together. Thus lead monoxide con-
tains one atomic weight (207 grams) of lead, combined with
one atomic weight (16 grams) of oxygen. Its composition is
therefore given by the expression PbO. This is called the
formula of lead monoxide. Lead sulphide, which contains
one atomic weight each of lead and sulphur, receives the for-
mula PbS. The formula of cupric oxide is CuO for the
same reason. But cuprous oxide, which contains two
atomic weights of copper to one of oxygen, has the
formula CU2O. In the same way cupric sulphide is CuS
and cuprous sulphide CU2S. Notice that a symbol is
multiplied by a small figure placed after it and below.
This figure multiplies only the symbol which immediately
precedes it.

117. Calcttlation of the Percentage Composition. — The
formula PbO means that lead monoxide contains 207 parts
of lead and 16 parts of oxygen in 207 + 16 or 223 parts.

90 AN INDUCTIVE CHEMISTRY

The percentage of lead must be

207

223

X 100 = 92.82

that of oxygen — X 100 = ^—

223 100.00

In cuprous sulphide there are 63.5 X 2 = 127 parts of
copper and 32 parts of sulphur, making 159 parts in all.

127
The percentage of copper is — X 100 = 79.87,

xoy

that of sulphur J? x 100 = J^ili

159 100.00.

The term atomic weight appUes only to elements. There

is no such thing as the atomic weight of a compound.

The sum of the atomic weights of the symbols in the formula

is called the molecular weight. 223 is the molecular weight

of lead monoxide (PbO) and 159 is the molecular weight of

cuprous sulphide (CU2S).

118. Calculation of the Formula from the Percentage Composition. —
In fixing the formula of a compoimd, its composition must first be
determined by methods similar in principle to those we employ in the
laboratory. Thus by heating a weighed quantity of silver with sul-
phur in a covered porcelain crucible, and weighing the silver sulphide
produced, we could show that it contained

12.90% of sulphur
87.10% of silver

Our problem is to express the quantity of sulphur in terms of the
atomic weight of sulphur and that of silver in terms of the atomic
weight of silver (108).

12.90 -^ 32 = .406

87.10 4- 108 = .806

Now .406 : .806 :: 1 : 2

Therefore silver sulphide contains two atomic weights of silver to one

of sulphur and its formula is Ag2S.

Hematite contains

30.00% oxygen

70.00% iron

30 ^ 16 = 1.876

OXIDES OF FAMILIAR METALS 91

The atomic weight of iron (see table) is 56

70 ^ 56 = 1.25
1.25 : 1.875 :: 2 : 3

The formula of Hematite (ferric oxide) is FeaOs.
Magnetite contains

27.59% oxygen
72.41% iron
27.59 ^ 16 = 1.724
72.41 -^ 56 = 1.293
1.293 : 1.724 :: 3 : 4
The formula is Fe304.

The student should have no difficulty in proving the formulas of
cinnabar, zinc blende and pjrite from the percentages given on pp. 84, 85.

119. Formulas of the Oxides and Sulphides already Studied. — ^The
following table gives the formulas of the oxides and sulphides already
studied.

Svlphidea

Oxides

•

Lead sulphide

PbS

Lead monoxide

PbO

Mercuric sulphide

HgS

Red lead

Pb804

Zinc sulphide

ZnS

Lead dioxide

Pb02

Cupric sulphide

CuS

Mercmic oxide

HgO

Cuprous sulphide

CU2S

Mercurous oxide

Hg20

Chalcopyrite

CuFeS2

Zinc oxide

ZnO

Silver sulphide

Ag2S

Cupric oxide

CuO

Iron monosulphide

FeS

Cuprous oxide

CU2O

Pyrite

FeS2

Silver oxide

Ag20

Ferric oxide

Fe208

Magnetite

Fe804

120. Equations. — Mercuric oxide is decomposed by heat:
Mercuric oxide — ^ mercury + oxygen.

Using our symbols, this becomes:

HgO — ^ Hg + O.

This equation has a precise quantitative meaning. It
means that 216 grams of mercuric oxide will yield 200 grams
of mercury and 16 grams of oxygen. Problems relating to
the amount of oxygen which can be obtained from a given
weight of mercuric oxide can be solved at once from the

92 AN INDUCTIVE CHEMISTRY

equation. What weight of oxygen can be obtained from 27
grams of mercuric oxide? The solution is

16
-— X 27 «= 2 grams of oxygen.

If we want the volume of the oxygen in liters we have only to
divide 2 grams by the weight of 1 liter of oxygen (p. 54)
1.43 grams.

2 -^ 1.43 = 1.4 liters at 0** and 760 mm.

How much mercuric oxide is needed to make 20 grams of
mercury? The solution is

216

— X 20 = 21.6 grams of mercuric oxide.

Definitions

Storage battery. An electric battery which, when exhausted, can
be charged, by connecting it with a dynamo, and used again and
again as a source of electric current.

Rhornbohedron, A crystal bounded by six equal rhombic faces
(Fig. 26).

Concentration. The closeness with which a substance is packed;
the quantity of a substance in unit of volume. For instance, the
concentration of oxygen is greater in pure oxygen than in air, and
still greater in compressed oxygen.

Atomic weight, (1) The quardityj in grams, in which an element
enters into its compounds. (2) The weight of the atom of an ele-
ment, if the value i6 is assigned to the weight of the atom of oxygen.

Symbol^ The first letter or the first two letters of the name of
an element. It means: (1) the atomic weight of the element, taken
in grams; (2) the atom of the element.

Formida. (1) A group of symbols which gives the composition
of a substance in parts by weight. (2) A group of symbols which
represents the molecule of a substance, each symbol representing
an atom.

CHAPTER VIII

OXIDES OF NON-METALS ALREADY STUDIED: SULPHUR

DIOXIDE, SULPHUR TRIOXIDE, CARBON DIOXIDE,

CARBON MONOXIDE, CARBON SUBOXIDE

121. Stilphur Dioxide. — We have noted (p. 55) that sul-
phur bums in oxygen, yielding a colorless gas with an irri-
tating smell. Since both substances are elements, this can
only be a case of combi-
nation. The gas pro-
duced is called sulphur
dioxide^ because it con-
tains two atomic weights
of oxygen. It can be
obtained in a fairly pure
state by means of the

apparatus

Fig. 27. — ^Preparation of sulphur dioxide by
burning sulphur in oxygen.

shown in
Fig. 27.
The sul-
phur in
■ the bulb is

I gently heated. A slow current of oxygen

I comes from a cylinder of the compressed gas.

I Sulphur dioxide cannot be collected over

I water, for one volume of water dissolves about

^^— »^^ 50 volumes of it at room temperature. Being
)^^^^^yr more than twice as dense as air, it is col-

^ ^ lected by nmning it into the bottom of a

FiQ. 28.— Proof jjy cvlinder, so that the air is forced out at

that oxygen "^
yields its own the top.

volume of sui- 122. SulphuT Dloxide Contains its own

Volume of Oxygen. — An important fact about
the burning of sulphur can be learned from the experiment
shown in Fig. 28. The retort is filled with oxygen and dips

AN INDUCTIVE CHEMISTRY

into mercury, the level of which is slightly higher inside to
allow for some expansion of the oxygen by heat. The bit
of sulphur at A is heated gently till it bums. At first the
expansion due to heat drives the mercury down a little, but,
when the retort cools, the level is the same as at first. The
oxygen has produced its own volume of sulphur dioxide. When
oxygen combines with sulphur the relation, by volume, of
the oxygen to the sulphur dioxide is 1:1.

123. Quantities by Weight. — Let us now consider the
quantities by weight in which oxygen and sulphur unite.
We can predict that 32 X x grams of sulphur will combine

FiQ. 29. — Composition of sulphur dioxide by weight.

with 16 X y grams of oxygen, and that x and y will be small
whole numbers.

Information about the values of x and y can be obtained
by the experiment shown in Fig. 29. A gentle stream of
oxygen is passed through the apparatus in the direction in-
dicated by the arrows. A weighed quantity of sulphur is
burned in the little porcelain vessel V, and the sulphur
dioxide is all absorbed by a strong solution of potash lye
(chemical name potassium hydroxide), placed in the U-shaped
tube, which is weighed before and after the experiment. If
one gram of sulphur is taken, it is found that the increase
in weight of the U-tube is 2 grams. This means that 2 grams
of sulphur dioxide have been formed:

1 gram sulphur imites with 1 gram oxygen, therefore 32
grams (1 atomic weight of sulphur) unite with 32 grams (2

OXIDES OF non-metals 95

atomic weights) of oxygen. Therefore, if x = 1, t/ = 2, or,
the formula of sulphur dioxide is SO2.

There is one thing taken for granted in this reasoning: that
X = 1, that is, that there is really one atomic weight of sul-
phur in sulphur dioxide. Our experiment shows only that

X : y :: 1 : 2.

Thus if there were 2 atomic weights of sulphur in sulphur
dioxide, there would be four of oxygen and the formula
would be S2O4. Since this represents exactly the same
proportions by weight of the two elements as the formula
SO2, our experiment does not decide between the two.

The reasons for regarding SO2, and- not some multiple of
it, as the correct formula, will be given later. In the mean-
time, notice the general fact that the simplest formula an-
swers most purposes of practical calculation, especially by
weight. For instance, in calculating how much sulphur
must be burned to yield a desired weight of sulphur dioxide,
it makes no diflference whether the formula SO2, or some
multiple of it, is taken as a basis.

124, Properties and Uses. — Sulphur dioxide is more easily
condensed than most other gases. At -8®, under atmospheric
pressure, or at room temperature (20**) under a pressure of
3 J<i atmospheres, it becomes a colorless liquid which is sold
in iron cylinders, or in siphon bottles of glass or metal, and is
used in bleaching wool and silk. This liquid absorbs much
heat when it evaporates and has been used as the working
liquid in one kind of ice machine. However, the anunonia
machine (Chap. XIII) is the usual type.

Sulphur dioxide is an excellent disinfectant, and was
formerly much used for this purpose, but, on account of
its destructive action on colored fabrics and metal sur-
faces, it has been displaced by formaldehyde (Chap. XIV).
It is poisonous to animals, but its odor gives warning of its
presence and accidents with it rarely occur. It is much
more dangerous to plants. Even traces of it in the air

96 AN INDUCTIVE CHEMISTRY

have a most mjurious effect upon vegetation. This is
especially true of evergreen timber, like pine, hemlock and
spruce.

The great use of sulphur dioxide is for the preparation of
sulphuric acid, the most important of all non-metallic
chemical products. For this purpose, sulphur dioxide is
made by burning pyrite, FeSi, which is far cheaper than
sulphur.

125. Sulphur Triozide. — Sulphur U^inde, SO*, is made
by the union of sulphur dioxide with another atomic weight of
oxygen.

SOs + O Z^ SO,

This combination is very slow, but in the presence of finely
divided platinum or of ferric oxide it becomes, at 400°, rapid
enough to serve as
A s •* the basis for the

^ tf ^ '^ ^ — ^ commercial pro-

duction of the
trioxide.

Fig, 30 shows a
lecture-table illus-
tration of the
formation of sul-
phur trioxide.
Sulphur bums at
S. By running
water out of the
F... a-r.™.,,.. ., -ph., «.dd. „^ „.,h„ " P P " bottle.

dioxide and oxyieo. CnOUgh aiT IS

drawn over the
sulphur to provide an excess of oxygen. At A is a wad of
asbestos which has been coated with finely divided platinum.
When this is gently heated, a dense white cloud of sulphur
trioxide appears in the bottle, where it is slowly absorbed
by the water.

OXIDES OF NON-METALS 97

126. Catalytic Action. — In this experiment the platinum
remains michanged. If it was consmned in the reaction,
the method could not be used commercially, since
platiniun is very expensive, much more so than gold. The
function of the platinum is merely to hasten a process
which would take place without its aid, if time enough were
allowed.

Cases of this kind, in which a substance alters the speed of
a change, without seeming to enter into it as one of the react-
ing substances, are nmnerous, as we shall see. They are of
special interest from the practical point of view, because,
since the substance acting in this way is not consimied, the
best material for the purpose can be employed, no matter
how costly. A special noun, catalysis, has been coined as a
class name for action of this sort. The corresponding adjec-
tive is catalytic, and the substance is called the catalyzer.
The term contact action is often used with the same meaning
as catalysis. The preparation of sulphur trioxide on a
large scale by the method we have just discussed is called the
contact process.

127. Properties of Sulphur Trioxide. — Sulphur trioride is
sold sealed up in glass bulbs. It is a mass of pure white,
silky needles, resembling asbestos. When exposed, it gives
oflf a dense, white, suflfocating smoke, and absorbs water
from the air, passing into a colorless, oily liquid which is sul-
phuric acid. The chief use of sulphur trioxide is for the
preparation of sulphuric acid (Chap. XX). It reacts with
water so violently that great care must be taken in bringing
the two together.

In the production of sulphur trioxide, two volumes of sul-
phur dioxide unite with exactly one volume of oxygen. The
reaction is reversible, as the arrows indicate (§125). If sul-
phur trioxide is heated to 900°, it separates completely into
the dioxide and oxygen. Even at 700° about 40% of it is
decomposed. For this reason, the temperature must be
maintained carefully at 400**.

AN INDUCTIVE CHEMISTRY

128. Soda Water. — ^When soda water runs into the
glass, the rapid rise of bubbles to the surface shows that a
gas is escaping. A siphon bottle of soda water affords a
means of collecting some of this gas (Fig. 31). A rubber
tube is slipped over the nozzle and the bottle inverted. The
gas is collected over water, though there will be some loss
by solution. It proves to be colorless and odorless, but it has

a sharp, pungent taste — ^the refreshing flavor of
effervescing drinks is due to it, the taste being
modified by the presence of other materials. A
flame lowered into the gas is extinguished as
though dipped into water.

Limewater is a colorless liquid, used in medi-
cine. It is made by slaking a little lime with
much water, and pouring off the clear liquid,
after the excess of slaked lime has settled. A
little limewater, poured into a bottle of the
soda-water gas, at once becomes cloudy; a
white solid containing lime has separated in the
liquid. Since no other gas, which could well be
confused with it, gives this result, we may use
the reaction with limewater as a test for the soda-water gas.

129. Composition of Carbon Dioxide. — ^We heat a piece
of charcoal in a spoon and lower it into a jar of oxygen.
Energetic combustion gives evidence of a chemical change.
This can only be a combination of the two substances, since
both are elements. When it is over, some or all of the char-
coal has disappeared and the jar contains an invisible gas
which renders limewater cloudy and extinguishes flame.
The same gas which escapes from soda water is formed by the
burning of charcoal in oxygen. Graphite and diamond bum
in oxygen to the same gas, and equal weights of charcoal,
graphite and diamond form equal weights of the compound.
This is a final proof that charcoal, graphite and diamond
are three forms of the same element, carbon. The gas formed
is called carbon dioxide.

Fia. 31.--A si-
phon bottle
for soda
water.

OXIDES OF NON-METALS 99

130. Fonnula of Carbon Dioxide: Volumetric Method. —
There are two ways of gettii^ quantitative knowledge: by
measuring volumes (volumetric method), and by working
with weighed quantities and weighing the products (gravi-
metric method). We had examples of both under sulphur
dioxide (pp. 94, 95).

Let us try the volumetric method first. Like sulphur, car-
bon combines with oxygen without changing the volume of
the latter— the volume of the carbon dioxide is equal to that
of the oxygen used up. This can be shown by
the apparatus illustrated in Fig. 32. The
vessel contains oxygen, confined by mercury
in the narrow lower part. The platinum wires
which pass through the glass are connected
by a spiral of platinum wire in which is shpped
a stick of charcoal. An electric current, sent
through the spiral, heats it red-hot and sets
fire to the charcoal. When the apparatus is
cold, the level of the mercury is the same as
it was before the combustion.

Accordingly, a liter of oxygen, if enoi:^)i pia.32—pioot
charcoal was burned in it, would form a liter that oiygen
of carbon dioxide. We have seen that the TOtume'of om^
weight of a liter of oxygen is 1.429 grams, bondjouiie.
The weight of a liter of carbon dioxide is 1 . 965
grams. The difEerence, 0.536 gram, is the weight of the
carbon. Now the atomic weight assigned to carbon by an
extensive study of carbon compounds is 12. How much
oxygen is combined with this weight of carbon in carbon
dioxide?

0.536 : 1.429 :: 12 : x .. a; = 32.
Since = 16, the formula is COj.

131. Gravimetric Mediod. — The gravimetric method con-
firms this. The principle is exactly the same as that of the
experiment in which we determined the composition of sul-

100

AN INDUCTIVE CHEMISTRY

Oxgg^n

Oxidhtd
Copper Qauz*

Potath Bulb
Fia. 33. — Composition of carbon dioxide by weight.

phur dioxide (Fig. 29). The apparatus is shown eonnected,
in Fig. 33, and an enlarged view of the vessel (potash bulb)
used for absorbing the carbon dioxide is shown in Fig. 34.
The gas passes through it from left to right. The lower

bulbs are half-filled
with a strong solu-
tion of potash lye
(chemical name po-
tassium hydroxide),
which absorbs the
carbon dioxide com-
pletely. The absorp-
tion apparatus is weighed before and after the experi-
ment.

Suppose that 1 gram of pure charcoal has been burned,
and that the increase in weight of the potash bulb is 3.667
grams. Then 2.667 grams of oxygen have united with 1
gram of carbon.

1 : 2.667 :: 12 : x .'. X = 32

Again the simplest formula is CO2. Our proof rests upon
the statement that C = 12, which we have taken for granted.
We shall consider later the proof ^

that CO2, and not some multiple of
it, is the correct formula.

132. Properties of Carbon Dioxide.
— At -79** carbon dioxide passes,
under a pressure of one atmosphere,
into a colorless hquid of about the
density of water. At 0°, 35 atmos-
pheres are required to liquefy it; at
room temperature (20**), 60 atmos-
pheres; and at 31% 70 atmospheres. Above 31** no pressure,
however great, will produce liquefaction, although the gas
may be compressed into a smaller volume than the Uquid
would occupy at a lower temperature. 31** is called the

FiQ. 34.— Potash bulb.

OXIDES OF NON-METALS 101

critical temperature of carbon dioxide. It is the highest
temperature at which the gas can be Uquefied.

Each gas has its critical temperature, above which it
cannot be changed into a liquid. For oxygen, this tempera-
ture is -118**. Before this was understood, pressures up to
3000 atmospheres were applied to oxygen at room tempera-
ture, in unsuccessful attempts to liquefy it. The critical tem-
perature of nitrogen is -146**, so that, like oxygen, it re-
quires great cold, along with pressure, to liquefy it. On the
other hand, the critical temperature of sulphur dioxide is
high (155**), and it is easily liquefied by pressure alone at or-
dinary temperatures.

When a cylinder of liquid carbon dioxide is opened, the
liquid rushes out, and at once evaporates. This produces
such intense cold, that a portion of it is frozen to a solid,
which resembles snow. Solid carbon dioride has a tempera-
ture of -80**. It may be placed lightly on the hand or tongue
without danger, but, if squeezed into close contact, freezing
of the flesh and injury result. Mixed with alcohol or ether it
makes a powerful freezing mixture.

133. Uses of Carbon Dioxide. — Liquid carbon dioxide
is sold quite cheaply in strong steel cylinders. These cylin-
ders are employed in charging soda water and other drinks
with the gas. At Saratoga, N. Y., and elsewhere, the car-
bon dioxide which streams from the earth is collected and
Uquefied by compression pumps. The gas is one product
of fermentation, and the great quantities which are formed
in the fermenting cellars of breweries are often utilized.
Carbon dioxide is an excellent fire extinguisher, and it has
been proposed to distribute the liquid in cities by systems of
pipes, just as is now done with water, and have it ready
everywhere for this purpose, but the suggestion has never
been followed.

134. Sources of Carbon Dioxide. — Carbon dioxide is con-
tained in the gases from volcanoes. Large quantities of the

gas issue from the earth in some localities. Near Naples is
8

102 AN INDUCTIVE CHEMISTRY

a cave called the Grotto del Caney which has a depression,
about two feet deep in the floor. This sunken portion is
kept full of carbon dioxide by a natural outflow. Dogs which
venture into it are suffocated, while a man walks about un-
harmed, because his head is above the level of the dense gas.
Death Valley, in Java, is a little wooded hollow in which
many wild animals are killed in the same way.

About a bilUon tons of coal are mined and burned each
year. That carbon dioxide is formed by the burning can
be proved by sucking out some of the gas from the smoke
pipe of a furnace in such a way that it bubbles through lime-
water. From the equation

C + O2 — >- CO2,

making the assumption that coal contains, on an average,
75% of carbon, we can make a rough estimate of the weight of
carbon dioxide thrown into the air each year from this source.

44
1 X 0.75 X — = 2f biUion tons.

The fact that limewater becomes cloudy when- we blow
through it by means of a glass tube proves that carbon di-
oxide is contained in the gas from the lungs (4.4% by
volume) . It is impossible to make an estimate of the amoimt
of carbon dioride which gets mto the atmosphere from the
breathing of animals, but the quantity must be very great.
Each man, for instance, produces about 800 grams of it per
day, and the population of the world is nearly 15 X 10*.
This means a yearly production of nearly 220 million tons
(metric) by the respiration of the human race alone.*

135. The Carbon Dioxide of the Atmosphere. — To these
prodigious quantities of carbon dioxide cast into the atmos-
phere we must add unknown but very large amounts for the
respiration of the lower animals and the higher plants, for

* The metric ton is 2204 lbs. In these rough calculations it may
be taken as equal to the avoirdupois ton.

OXIDES OF NON-METALS 103

plants continually give off small quantities of the gas. It is a
product of the decay of animal and vegetable matter, and the
amount which gets into the air from this source must be very
great. We must recall also the carbon dioxide of volcanic
gases and the constant streams of it which escape in certain
localities, like those m^itioned in the two preceding sections.

The total quantity of carbon dioxide in the atmosphere is
enormous. But the weight and volume of the atmosphere are
so immense that the percentage of carbon
dioxide is small ( . 03% by volume or 3 parts
in 10000). Since this percentage does not
increase there must be some process in
operation which takes the carbon dioxide
out of the air about as fast as it enters from
the sources just mentioned. How this re-
moval of carbon dioxide is effected is shown
by the experiment illustrated in Fig. 35.

The fiask contains sprigs of fresh mint,
Ciovered with water which has been saturated
with carbon dioxide. The test tube is filled
with the same liquid. Nothing happens in
the dark, but in sunlight bubbles of gas
rise and collect in the test tube. The spark
test shows that the gaa is oxygen. That the
oxygen comes from the carbon dioxide can Fiq. as.— Formflii™
be proved by using water freed from dis- °,av^"^friflnu! ""
solved gases by boiling. Under these con-
ditions, no oxygen is formed. The water merely serves the
purpose of making it easy to collect the oxygen.

The experiment can be varied by packing a fiask with
mint and passing carbon dioxide into it until the air is all ex-
pelled. When the arrangement is exposed to sunlight, oxy-
gen is formed, which can be separated from the carbon di-
oxide by a solution of potash lye (potassium hydroxide)
which absorbs the latter. Other fresh green leaves can be
used, instead of mint, in both experiments.

104 AN INDUCTIVE CHEMISTRY

136. The Cycle through Which Oxygen Passes. — ^These
results show that, in sunlight, the green leaves of plants de-
compose carbon dioxide and return the oxygen to the air.
The carbon is built up mto complex compounds which ul-
timately form the structure of the plant. We may represent
the stages through which the carbon passes in natiu-e by a
triangle:

Atmosphere

Animals •< — Plants

The meaning is that the carbon of the animal body is oxidized
into carbon dioxide and cast into the air. Thence the carbon
is absorbed by plants, which build it up into their tissues.
When these are eaten by animals, the cycle begins anew.
After the death of an animal or a plant, the carbon is con-
verted into carbon dioxide during decay, and returned to the
atmosphere.

The cycle through which oxygen passes in nature can be
represented by a quadrilateral.

Oxygen
of Air

Plants <s.D B > Animals

Carbon dioxide
of air

This means that the oxygen of the air is taken up by animals
who cast into the atmosphere a liter of carbon dioxide for
every liter of oxygen which they consume. This carbon

OXIDES OF NON-METALS 105

dioxide is decomposed by the plants, which return the oxygen
to the air, and the cycle begins again. It is probable, though
far from certain, that the plants restore to the atmosphere
just about as much oxygen as the animals (including man)
remove from it by combustion and respiration. Fairly exact
analyses of the air have been made for the last seventy-
five years, but they have not shown any permanent change in
the percentages of oxygen or of carbon dioxide. Air which
had been sealed up in vases in the ruins of Pompeii for nearly

CO.

^-^

^[^^^'^'.-^'^y^'.'^^A-^T^'.'.i, ' — Q^ (y

Fig. 36. — ^Action of heated zino on carbon dioxide.

two thousand years proved, when examined by Liebig, to
have the same composition as the present atmosphere.

137. Action of Carbon Dioxide upon the System. — Carbon
dioxide is not poisonous. The workmen in the fermenting
cellars of breweries continually breathe air containing 2%
or more without damage: 5% is injurious and much more
than that rapidly causes death by suffocation. When the
body is plunged into a vessel containing carbon dioxide, the
head being left free so that pure air is inhaled, there is at
first a tingling sensation of warmth over the skin. This is
followed by such alarming collapse that the experiment must
be discontinued.

138. Carbon Monoxide, CO. — ^When burning magnesium
is lowered into a jar of carbon dioxide, the combustion con-
tinues and white magnesium oxide mixed with carbon
(lampblack) is produced. But when a stream of carbon
dioxide is passed over hot zinc dust. Fig. 36, the zinc turns to
white zinc oxide, but no lampblack separates. Instead, a

106 AN INDUCTIVE CHEMISTRY

colorless gas issues from the tube and can be collected over
water, in which it is very slightly soluble. This gas does not
render limewater turbid, so it is not carbon dioxide. When
a flame is applied, the gas takes fire and bums with a blue
flame, exactly like that which plays over the surface of
a coal fire. The product of the burning is carbon dioxide,
for the contents of the vessel after the flame has died out
render limewater white and opaque.

The zinc has removed half of the oxygen from the carbon
dioxide, producing carbon monoxide, CO:

CO2 + Zn — >• ZnO + CO,

and the carbon monoxide has combined again with oxygen
when the flame was applied:

CO + — ^ CO2.

Carbon monoxide would also have been obtained if the tube
had contained red-hot charcoal instead of zinc:

CO2 + C — ^ 2C0.

This last reaction occurs in a coal fire. Next the grate, where
the air supply is abimdant, the coal bums to carbon dioxide.
This, as it passes up through the column of glowing coal,
changes to carbon monoxide, which finally bums again to
carbon dioxide at the top of the fuel bed, where it meets
more air. If the fire is not well-handled, carbon monoxide
will escape up the chimney, which means great waste of fuel.
In many works it is the practice to analyze the chimney gases
constantly. The firemen are fined when carbon monoxide is
present, and premiums are paid them when it is absent and
the composition of the gases shows that good work is being
done.

139. Effect of Carbon Monoxide Upon the Body. — Fatal accidents
often occur when the gases from stoves or furnaces are allowed to enter
sleeping-rooms. The explanation is that carbon monoxide is intensely
poisonpus, 0.5% of it being rapidly fatal and much less by prolonged
inhalation. This is due to the fact that it combines with the coloring

OXIDES OF NON-METALS 107

matter (hsemoglobin) of the red blood corpuscles, forming a compound,
and preventing them from doing their work of carrying oxygen about
the body. Carbon monoxide poisoning is therefore a kind of suffoca-
tion and 10 c.c. of it per kilogram, reckoned on the weight of the animal,
is enough to cause death. Traces in the air cause violent headaches
and nervous symptoms. Being odorless, it gives no warning of its
presence, and insensibility comes so quickly that it is usually impossible
for the victim to reach a door or window. The poisonous action of
illuminating gas is due to carbon monoxide (up to 40% in modern gas).
The gas connections of a house should be carefully looked after. Small
leaks can be detected by the bubbling which follows when soapy water
is smesired over the suspected joint. The use of gas radiators, es-
pecially in sleeping-rooms and bath-rooms, is dangerous.

The treatment of carbon monoxide poisoning is about the same as
that used in cases of apparent drowning: fresh air, oxygen if avail-
able, artificial respiration, and a physician at the earliest possible
moment.

If an animal is put in air under a pressure of ten atmospheres, as much
as 6% of carbon monoxide can be mixed with the air without causing
any s3rmptoms of poisoning. At the high pressure, enough oxygen
to support life dissolves in the plasma of the blood, and the fact that
the corpuscles no longer supply oxygen makes no difference.

Carbon monoxide has about the same specific gravity as air.
Cold and pressure convert it into a liquid which boils at -190°.

140. Combination of Gases by Voltime. — A mixture of carbon
monoxide and oxygen explodes when flame or electric sparks
are applied, produc'ng carbon dioxide. Information about the
volumes of the two gases which unite can be obtained (a) by calcu-
lation from the quantities by we'ght (b) by direct measurement.

(a) From the equation,

CO + — >- CO2

we note that 12 + 16, or 28, grams of carbon monoxide unite with
16 grams of oxygen, producing 44 grams of carbon dioxide. The
weight of 1 liter of carbon monoxide is 1 . 25 grams. The volume
of these 28 grams will be

:: — r =22.4 lite^s^
1.25

^ In all calculations of this kind the gases are supposed to be at the
standard temperature 0** and the standard pressure of 760 m. m

108

AN INDUCTIVE CHEMISTRY

Since the weight of a liter of oxygen is 1 . 429 grams, the volume
of the 16 grams of oxygen will be

1.429

= 11.2 liters.

The weight of 1 liter of carbon dioxide is 1 . 965 grams and the
volume of the 44 grams will be

1.965

= 22.4 liters. Therefore

22 . 4 liters of
carbon monoxide

11. 2 liters of

22.4 liters of
carbon dioxide.

oxygen

Dividing through by 11.2 and writing volumes instead of
liters, we get

2 volumes of . 1 volume of ^ 2 volumes of

carbon monoxide

oxygen

carbon dioxide.

(b) Direct measurement confirms this. A eudiometer is a
graduated glass tube (Fig. 37). In the upper part are two
platinum wires, between which a spark can be passed. 20 c.c.

of carbon monoxide and 10 c.c. of oxygen are
allowed to enter the tube. The level of the
mercury in both limbs must be made the
same when the measurements are taken.
Then the spark is passed. There is an ex-
plosion, and 20 c.c. of gas remain. This
_ can be proved to be carbon dioxide by

H H letting a little potash lye pass up into the

H H tube. The gas is completely absorbed.

H Ib^ '^'* General Statement. — We are now

^^^^^^^^ ready to make a general statement about the
^^^^ combination of gases by volume.

(1) When two gases combine there will be a
simple relation between their volumes,

(2) // the compound is also a gaSj there will
be a simple relation between its volume and

that of each of the gases which have united to form it.

The phrase "simple relation" sometimes offers difficulties to
the student. To say that there is a "simple relation" between

Fig. 37. — Synthesis of
carbon dioxide from
carbon monoxide
and oxygen.

OXIDES OF NON-METALS 109

two things means that they are equal, or that one is twice as
great as the other, or that one is to the other as 2 is to 3 and so
on. It means that there is a relation between them which can
be expressed by small whole numbers.

The law expressed in (1) and (2) was stated by the French
chemist Gay LussaCj in 1808. It is called the law of combining
volumes. It applies only to ga^es. The instances we have
studied thus far are these:

1 volume of oxygen + solid sulphur — >- 1 volume of sulphur dioxide.

2 volumes of ,1 volume of , solid sulphur
sulphur dioxide oxygen trioxide.

1 volume of oxygen + solid carbon — >- 1 volume of carbon dioxide.

2 volmnes of ,1 volume of 2 volumes of

carbon monoxide oxygen carbon dioxide.

(1) The elements combine with each other in the quantities
indicated by the atomic weights, or in small multiples of those
quantities. But (2) they also combine in equal volumes, or
small multiples of equal volumes. Therefore (3), the atomic
weights (in grams) of the gaseous elements must occupy equal
volumes, or small multiples of equal volumes.

Oxygen and nitrogen are the only gaseous elements we have
studied upon which we can test this conclusion. We have just
noted (p. 108) that 16 grams of oxygen fill a volume of 11.2
liters. The atomic weight of nitrogen is 14 and the weight of
1 liter is 1 . 25 grams. Hence the volume filled by the atomic
weight will be i^= 11. 2 liters, which is identical with the
result obtained for oxygen. The same calculation for the other
gaseous elements would give the same result. The volume of
the atomic weight would be 11.2 liters.^ We shall not here
discuss the case of sulphur, mercury and many other ele-
ments, which exist as gases only at high temperatures.

142. Compound Gases. — Finally, a word about compound
gases. Of course there are no special atomic weights for com-
pounds. The sum of the atomic weights of the elements in the
formula gives the molecular weight of the compound, and

* This reasoning is based upon the behavior of the elements when
they form compounds. It has no bearing, therefore, upon argon and
the other elements which form no compounds.

110

AN INDUCTIVE CHEMISTRY

this is the weight of it which enters into chemical changes.
Let us repeat a few of the equations into which compounds
enter

SO2 + O — >■ SOs

CO + O — >- CO2

CO2 + Zn >- ZnO + CO

CO2 + C — >- 2C0

28 grams of carbon monoxide, 44 grams of carbon dioxide and
64 grams of sulphur dioxide are the molecular weights of those
substances, the quantities in which they enter chemical changes.
We have shown that 28 grams of carbon monoxide and 44 grams
of carbon dioxide each fill a volume of 22 . 4 liters. What about
the molecular weight of sulphur dioxide? One liter of the gas
weighs 2 . 86 grams. Hence 64 grams of it will fill a volume of

64
2.86

= 22.4 liters.

The molecular weights of all gases fill the same volume. This
volume is 22 A liters , if the unit of weight is the gram and the
pressure and temperature are standard.

To get an idea of this volume, think of a cube about the size
of a cubic foot. The side of this cube is 11 . 1 inches (28 . 19 cm.).

Such a cube would hold 22.4
liters. To determine the molec-
ular weight of any gas we should
only have to fill the cube at S.T.P.
(S.T.P. means standard temper-
ature and pressure) and find the
weight of the gas in it.

The cube is indicated reduced
to tV the real diameter in Fig.
38. The cube in the drawing
has ttjW the volume of the real
one and holds 22.4 c.c. The
molecular weights of all gases in
milligrams (1 milligram = 0.001 gram) would, at S.T.P., fill
the cube in the figure.

Since the relation between the gram and the ounce (avoirdu-
pois) is the same as the relation between the liter and the cubic

Fig. 38. — Standard cube which would
hold the molecular weights of all
gases, taken in milligrams.

OXIDES OF NON-METALS 111

foot, it follows that the molecular weights of all gases taken in
ounces will occupy 22 . 4 cu. ft. If we took the molecular weights
in pounds their volume would be 22.4 X 16 = 358.4 cu. ft.,
but the molecular weights of the different gases would still fill
the same volume. That is the essential thing, that the volumes
are the same for different gases. The number 22.4 is merely
an accident which depends upon the magnitude of the gram and
the liter.

143. Carbon Suboxide. — Carbon suboxide, C8O2, is at low
temperatures a colorless liquid with a strong irritating odor re-
caUing that of mustard. It boils at 7®. It is combustible.
When kept in a sealed glass tube, it changes to a dark red solid.

Definitions

CatalysL A substance which increases the speed of a chemical
change between other substances, but remains itself imaltered.

Catalyzer. Same as catalyst.

Catalytic action, A chemical change in which a catalyst is em-
ployed.

Contact action. Same as catalytic action.

Gravimetric analysis. Analysis by starting with a weighed sam-
ple, and weighing the products obtained from it.

Volumetric analysis. Analysis in which the results are obtained
by measuring volimies of gases or liquids.

Critical temperature. The temperature above which a gas cannot
be liquefied by pressure. When heated to the critical temperature,
a hquid is converted into vapor, no matter what the pressure may be.

Molecular weight. The sum of the atomic weights of the s3nnbols
in the formula of a substance.

CHAPTER IX

WATER AND HYDROGEN

144. Water in Nature. — About three-fourths of the sur-
face of our planet is covered with water. This water is in
constant circulation. It is evaporated from the oceans by
the sun's heat and blown over the land, on which, when
condensed by cooling, it falls as rain. Upon this constant
circulation, the plant life and animal life of the world depend.

Rain is the purest natural water, but even while in the air,
it absorbs gases and is contaminated with dust and bacteria.
When it reaches the surface of the earth, the water begins to
take up mineral matter from the soil and the rocks. Sea-
water contains more than 3% of dissolved matter, chiefly
salt. The waters of the Dead Sea and the Great Salt Lake
contain upwards of 25% of dissolved solids — so much that
aquatic life does not exist in them. River and brook waters
contain smaller quantities of mineral matter — ^usually much
less than 0.1%.

Mineral waters are spring waters which contain such large
quantities of dissolved material that they have a marked
flavor and a special action of some kind upon the body.

145. Purification of Water for Chemical Purposes. — The
impurities of natural water imflt it for laboratory uses. The
method of purification depends upon the fact that the water
is converted into steam at a temperature of 100 **, while the
mineral matter does not vaporize at all at that temperature.
Hence the steam, when passed through a cold tube, con-
denses to form water which is practically pure. Fig. 39 is a
diagram which illustrates the principle of the process. The
water is heated in a copper vessel B and the steam passes
through A and C into the spiral tube D of copper or tin,
which is cooled by water circulating outside it. Pure water
collects in 0. The mineral impurities remain in B. Glass

112

WATER AND HYDROGEN 113

vessels are not used because glass is decidedly soluble in
water. The process is called distillation. It is also used

for purifying other liquids. The apparatus used in the
laboratory, for preparing small quantities of distilled
water, is shown in Fig. 40.

Distilled water is not abso-
ItUdy pure. Traces of mineral

matter are contained in it, and "*

gases are alisorbed from the
air. In fact an "absolutely
pure subatajice" is lilce the
circle in mathematics, an ideal,
which real things approach,

but never reach. For very *»

careful work, water is purified
by several distillations, con-
ducted with special precau- oMii.Jwa,r
tion. Even then, all we can "■*"
do is to reduce the impuritits ™- '^ZlST.Tj^l.S'^ """
to such small quantities that

they do not affect the behavior of the water, and can not,
therefore, he detected in it.

146. Properties of Water. — Water is blue. The color is
faint> but it can easily be seen wh^i a porcelain bath-tub is

114 AN INDUCTIVE CHEMISTRY

filled, and in a layer two meters or more in thickness it be-
comes very distinct. This is one cause of the bluish color of
large bodies of clear water in lakes and in the ocean. Ice has
the same color, very noticeable in a glacier.

The properties of water fit it to serve as a standard sub-
stance in several important respects. Its freezing-point and
boiling-point under one atmosphere pressure give us the two
fixed points 0** and 100** of the centigrade scale. The cor-
responding points on the Fahrenheit scale are 32** and 212**.
The mass of a cubic centimeter of water at the temperature
at which water is densest (nearly 4**) is the unit of mass, the
gram. The amount of heat required to warm 1 gram of
water from 15** to 16** is the unit of the quantity of heat, the
calorie. Water at 4** is the irnit of specific gravity. The
statement that the specific gravity of platinum, for instance,
is 21.5 means that 1 c.c. of platinum weighs 21.5 times as
much as 1 c.c. of water at 4**.

147. Action of Magnesium on Water. — ^When we studied
air, we foimd that its behavior with metals at high tem-
peratures led us to an understanding of its chemical na-
ture. The fact that iron, zinc and other metals rust when
wet is a plain indication that water enters into a chemical
change with them. Let us try with water the same plan
which was successful with air.

A piece of magnesium ribbon bums brilliantly in air to a
white mass which weighs more than the magnesiiun and which
must consist of magnesium oxide. A beaker one-fourth filled
with water is covered with a perforated asbestos plate. The
water is boiled imtil the steam has expelled all the air and
burning magnesium is introduced. The combustion goes
on with undiminished brilliancy and the substance produced
has all the properties of the oxide formed by burning the me-
tal in air. This indicates that oxygen is one of the constitu-
ents of water. If the experiment is made in a dark room, a
pale flame can be seen, burning around the hole in the plate.
Assuming that water contains two elements, one of which is

WATER AND HYDROGEN

115

oxygen, it is plain that the other must be set free when the
oxygen combines with magnesium. It would seem that
the other constituent is a combustible gas, which is liberated
inside the beaker, and bums when it meets the oxygen of
the air outside.

148. Action of Zinc and Iron on Water. — A simple way of
investigating the behavior of zinc and iron with water is de-
scribed in the laboratory studies. Fig. 41 shows an experi-
ment for the lecture table. Steam is passed over hot pow-
dered zinc or iron contained in a hard glass tube. The gas
issuing from this tube is collected over water. The zinc
turns to white zinc oxide, while the iron forms the same blue-
black oxide (magnetite) which it yields when burned in air
or oxygen. A colorless gas collects over the water. This

Fio. 41. — ^Aotion of heated sine on steam.

is the other constituent of which we are in search. It is
called hydrogen. It is easily obtained by the method
described in the laboratory studies (interaction of zinc and
sulphuric acid).

149. Properties of Hydrogen. — ^When pure, hydrogen
is odorless. From the fact that we have collected it
over water it follows that its solubility in that liquid
must be small. An experiment like that described on
p. 72 shows that 100 c.c. of water at 0** dissolve
only 2 c.c. of hydrogen. When a liter flask full of air
is weighed, and then weighed again after the air has
been displaced by hydrogen, the flask is found to be
about 1.2 grams lighter than before. Hydrogen is

116

AN INDUCTIVE CHEMISTRY

FiQ. 42. — Synthesis of water.

much the lightest of gases. A liter of it at S.T.P.
weighs only 0.09 gram.

150. Liquefaction of Hydrogen. — Like all other gases
which are slightly soluble in water, hydrogen is hard to
liquefy. Sir James Dewar liquefied the gas in 1898 by sub-
jecting it to great pressure and cold (Chap. XIII). Liquid

hydrogen is colorless
and only tV as dense as
water. It is by far the
lightest of liquids. It
boils at -253 ^ A vessel
containing it becomes
covered, in a little while,
with a white layer of
solid air. . Dewar led
various gases through
tubes into vessels stand-
mg m liquid hydrogen.

All gases except hehmn became solid, and fell as snow

to the bottom.
When liquid hydrogen is made to boil rapidly by reducing

the pressure upon it by means of an air pump, so much heat

is absorbed that the liquid freezes to a mass resembling ice.

Solid hydrogen has about the same density as the liquid

and is the lightest of solids.

151. More About the Composition of Water. — Henry
Cavendish, who was born in 1731 and died in London in 1810,
was the first to point out that hydrogen is an element. He
called it "inflammable air.'' He was also the first to show
that, when it combines with oxygen, water is the only prod-
uct. When dry hydrogen is burned imder a cold inverted
jar the glass is covered with fine drops of water. That this
results from the combustion of the gas is shown by the fact
that the deposit is not produced when the hydrogen, without
being lighted, is simply allowed to escape under the jar.
20 or 30 c.c. of water can be quickly obtained by the

WATER AND HYDROGEN 117

experiment shown in Fig. 42. Hydrogen is burned in
a flask immersed in water to keep it cold. Oxygen
is run into the flask through a separate tube. Care
is required not to allow a mixture of the two gases
to form in the flask, as this would lead to an explosion.

152. Quantitative Data.— To obtain quanti-
tative information we may choose (a) the
volumetric or (b) the gravimetric method

(a) The apparatus is the eudiometer shown
in Fig. 43. We fill it with mercury and invert
it in a narrow cylinder containing the same
liquid. Then we introduce say 10 c.c. of
hydrogen and 10 c.c. of oxygen and pass the
electric spark between the platinum wires.
There is a slight explosion. Since the tube
is cold, the water which is formed condenses
to a liquid whose volume is so small that it
cannot be measured on the graduations.
5 c.c. of gas remain, which the spark test ^p„ttu^
shows to be oxygen. Thus 10 c.c. of hydrogen water by voi-
unlte with 5 c.c. of oxygen, or ""*■

2 Volumes of hydrogen + 1 Volume of oxygen — >- water,

The atomic weight of hydrogen is 1 .01 and the weight of a
liter at S.T.P. is 0.09 gram. The volume at S.T.P. of the
atomic weight will be

1.01

— — = 11.2 liters.

0.09

We have seen that the volume of the atomic weight of oxygen
(16 grams) at S.T.P. is also 11.2 liters. Therefore, at S.T.P.

11.2 liters X 2 + 11.2 liters — >■ water
2 atomic weights 1 atomic weight
of hydrogen of oxygen

Therefore the simplest formvla of water is HtO.

118

AN INDUCTIVE CHEMISTRY

(b) Hydrogen, at a red heat, removes the oxygen from
many oxides of the metals, forming water and setting free
the metal. For example:

Cupric oxide + Hydrogen
Magnetite + Hydrogen

- Copper + Water
Iron + Water.

A gravimetric method for ascertaining the composition of
water can be based upon this behavior. The apparatus is
shown in Fig. 44. 'The combustion-tube contains cupric
oxide. It is disconnected and weighed before and after the
experiment. The absorption tubes are also weighed before
and after the experiment. They are intended to collect the
water formed. Most of the water condenses in the bulb and
the rest is caught by the U-tube, which contains glass beads
wet with strong sulphuric acid, which eagerly absorbs

Hydrogen

Drying Agents

FiQ. 44. — Composition of water by weight.

water. Pure dry hydrogen is led through the apparatus
from left to right and the cupric oxide is heated to faint
redness.

After the experiment, the combustion-tube contains cop-
per, and its loss in weight is the oxygen which has combined
with the hydrogen to form water. The weight of this water is
obtained from the gain of the absorption tubes. Suppose that
the loss in weight of the combustion-tube = 1 gram, and that
the gain of the rest of the apparatus = 1 . 1263 gram. Then
the hydrogen which formed water = . 1263 gram, and

WATER AND HYDROGEN 119

the weight which would unite with 16 parts of oxygen is
given by the proportion

1: 0.1263 :: 16 : X ,\ x = 2.02 grams.

Since the atomic weight of hydrogen is 1 .01, this means two
atomic weights, and the simplest formula is HjO.

Related Topics

153. Iron Oxide and Hydrogen. — When powdered mag-
netite is used in the experiment of Fig. 44, water is formed
in the same way and iron is left. But we saw on page
115 that iron powder will attack steam, setting free hydro-
gen and forming magnetite. It seems, therefore, that the
reaction

Iron + steam ^ ^ magnetite + hydrogen

is reversible, like the formation of silver oxide (p. 83). In this
case, also, the explanation is obtained by a study of the influence
of concentration on the progress of the change.

(1) When steam is passed over heated iron, the liberated
hydrogen is swept away at once and has no chance to act upon
the iron oxide which is formed. The concentration of the hydro-
gen is kept low. But the concentration of the steam is kept
high. Hence it acts upon the iron until the metal is all converted
into oxide.

(2) When hydrogen is passed over heated iron oxide, the
process is reversed. The constant supply of hydrogen keeps its
concentration high. The steam is removed as fast as produced, so
that its concentration cannot rise much above zero. Scarcely any
steam is offered to the iron, while hydrogen is generously offered
to the iron oxide. Hence the oxide is converted into the metal.

We may build a general statement on this basis. In a re-
versible changCy an increase in the concentration of a substance
causes the change to proceed in the direction in which that sub-
stance is consumed. Thus, in this case, if the concentration of
the steam is increased, iron oxide and hydrogen are formed,
which consumes some of the steam. If the concentration of the
hydrogen is increased, iron and water are formed and some of
the hydrogen disappears.

120

AN INDUCTIVE CHEMISTRY

154. Use of Hydrogen in Analyzing Air. — Suppose we had a
measured volume of air, confined over water. If a hydrogen
flame was introduced, it would go on burning till the oxygen was
used up, and would then be extinguished. The water formed
would condense and occupy a volume too small to measure.

Therefore the shrinkage in the volume of
the air would measure the quantity of
oxygen.

This method was used by Scheele. A
drawing of his apparatus is given in Fig.
45. He obtained the total capacity of the
flask by filling it with water and pouring
the water into a graduated vessel. The
water which entered during the combus-
tion, and which was equal in volume to
the oxygen which had disappeared, he
measured in the same way.

It is much more exact to mix hydrogen
with a measured volume of air in a
eudiometer (Fig. 43). A more conve-
nient style of eudiometer for the purpose is shown in Fig.
37. When the spark is passed there will be an explosion due
to the formation of water, which at once condenses. Water is
formed from two volumes of hydrogen and one volume of oxygen.
Hence, one-third of the shrinkage in volume is the oxygen,
which has disappeared.

Suppose that we took 16 . 7 c.c. of air and added enough hydro-
gen to make the total volume 29 c.c. After the explosion, the
volume was only 18.5 c.c. The contraction was 29 — 18.5 =
10.5 c.c. One-third of 10.5, or 3.5 c.c, is the volume of the
oxygen, and its percentage by volume is

FiQ. 45. — Burning hy-
drogen in a confined
volume of air.

3.5
16.7

X 100 = 20.95%.

155. Combustion. — The word combustion has about the same
meaning as the ordinary term burning. We have used it to
apply to rapid union with oxygen, accompanied by the produc-
tion of light and much heat. Oxygen is not the only gas which
may support combustion. A few substances burn in nitrogen

WATER AND HYDROGEN 121

and quite a number in hydrogen. Later, we shall study active
gases, like chlorine^ in which violent combustions occur.

However, combustion in the air is union with oxygen. In
anthracite coal and coke, it is chiefly carbon which burns. Soft
coal, wood, kerosene, gasoline, illuminating gas and candles
contain much hydrogen, in chemical union with carbon. When
they are burned, water and carbon dioxide are produced.

From the behavior of ordinary fuels it is clear that carbon
and hydrogen must produce great quantities of heat when they
unite with oxygen. Exact measurement shows that one gram of
carbon, when burned, produces enough heat to raise the tem-
perature of 83 grams of water from the freezing- to the boiling-
point. The corresponding number for hydrogen is 350. The
burning of one gram of hydrogen to water produces more heat
than can be obtained, by any other chemical process, from one
gram of material.

156. Rapid and Slow Combustion. — The rusting of metals
is mainly slow union with oxygen in the cold, that is, slow com-
bustion. Carbon burns slowly in the same way, though the
product is not a rust, but an invisible gas, carbon dioxide.
Samples of coal are usually sent to the chemist for analysis in
sealed fruit jars. In less than a week, all oxygen has vanished
from the air in the jar and united with the constituents of the
coal. Moissan sealed up charcoal powder with oxygen in glass
tubes and kept them at 100°. After a month he cooled one
end of the tube with liquid air. A snowy deposit of solid car-
bon dioxide (p. 101) proved that combination had taken place.
A similar slow combustion occurs in the body, where the carbon
and hydrogen of complex compounds unite with oxygen derived
from the blood. This is the source of the heat which keeps the
temperature of warm-blooded animals above that of their sur-
roundings.

We have seen (p. 24) that copper combines slowly with sul-
phur in the cold and that high temperature quickens the com-
bination until it becomes a combustion. We also found that
it was sufficient to heat one portion of the mixture of copper
and sulphur. The heat evolved at this point raised the tempera-
ture of the neighboring portions, and the whole mass was finally
transformed to copper sulphide without any further application

122 AN INDUCTIVE CHEMISTRY

of heat. The combination of carbon with oxygen is similar and
the accelerating effect of high temperatures supplies a complete
explanation of it.

The speed of a moving body is measured by the distance it
travels per second. The speed of a chemical process is measured
by the weight of material transformed per second. Measure-
ment shows that, on an average, the speed of a chemical change
is doubled by a rise in temperature of 10®.

There is no temperature at which coal begins to burn. It
burns very slowly in the coal bin and much more rapidly when
shovelled into the furnace, because its temperature is higher by
about 1000°. In order to appreciate the enormous effect that
this would have upon the speed of the combination consider
that:

A rise of 10® multiplies the speed by 2

A rise of 20** multiplies the speed by 2 X 2 = 2^

A rise of 30'' multiplies the speed by 2X2X2 = 2*

A rise of 1000** multiplies the speed by 2*''

2^^ is about equal to the number 126 followed by 28 ciphers.
Evidently the accelerating effect of high temperature is quite
competent to explain why coal combines so much more rapidly
with oxygen at a red heat.

The control of the furnace is effected, not by regulating the
temperature directly — which would be complicated from a prac-
tical point of view — but by controlling the rate at which ojtygen
is admitted to the fuel bed. No matter what the speed of com-
bination may become, the coal cannot combine with more
oxygen than is offered to it.

The slow combustion of coal, especially of bituminous coal,
is an important practical matter where thousands of tons are
stored. It often happens that enough heat is developed to set
fire to the mass. Even when this does not occur, the slow com-
bination with oxygen will, in a short time, seriously reduce the
heating value of the coal. Therefore large quantities of bi-
tuminous coal are best stored under water, to prevent the access
of oxygen.

157. Flames. — Sulphur burns in oxygen with a large pale
flame: iron burning in oxygen, gives a brighter light and a
higher temperature, but no flame is seen. The cause of this

WATER AND HYDROGEN

123

striking difference is that sulphur is much more easily con-
verted into vapor (more volatile) than iron. It boils at 448°,
which is below a red-heat; iron only at the temperature of the
electric arc. So the sulphur is vaporized by the heat of its
own combustion and its vapor streams out into the surrounding
space to meet the oxygen. This space becomes filled with a
mixture of hot sulphur vapor, sulphur dioxide and oxygen,
which makes up the flame.

Iron is not vaporized at all by the temperature produced when
it combines with oxygen. The oxygen must go to the iron, and
the combination takes place entirely at the surface of the metal.
The iron glows brightly, but
since the chemical change does
not extend into the surrounding
space, there is no flame.

It seems, then, that we have
a basis for two general state-
ments:

1. A solid which is not con-
verted into vapor or gas while
burning, will burn without flame.
If conversion into gas or vapor
takes place, a flame is formed.
Since the latter case is the more
common one, combustion with
flame is much more frequent
than without it.

2. A combustible gas will
always burn with a flame. This proposition is really included
under (1).

The laboratory work will afford material for testing the truth
of these statements.

158. Reversed Flames. — Hydrogen burns with a hot blue
flame in air or oxygen. Suppose we reverse the arrangement, de-
livering oxygen through a tube into a vessel full of hydrogen, what
would be the result? Since the same chemical change could occur,
we might predict that a very similar flame would be obtained.

A lamp chimney (Fig. 46) affords an inexpensive apparatus
for investigating the question. It is closed below by a rubber

Fig. 46. — Oxygen burning in hydrogen.

124

AN INDUCTIVE CHEMISTRY

stopper, bearing a tube to deliver the hydrogen. Illuminating
gas is cheaper and answers the same purpose. A perforated
asbestos plate is laid on the top to avoid breakage, and the gas
is lighted. A mouth blowpipe carrying a gentle current of
oxygen from a cylinder is lowered into the chimney. The

oxygen takes fire and continues burning
with a pale hot flame exactly like that
of burning hydrogen.

By means of the apparatus of Fig. 47 a
flame of air burning in illuminating gas
can be obtained. The right-angled tube
delivers the gas; the short wide tube is
open at both ends.

The stopper is taken out, the gas
turned on and lighted. When the stopper
is again inserted, the gas flame soon
exhausts the oxygen in the vessel; a pale
blue flame floats about the chimney for
a moment and then settles on the air
tube, where it continues to bum. This is
the flame of air, burning in illuminating
gas. It looks exactly like the Bunsen
flame. The gas may now be lighted at
the hole in the asbestos plate and we have above the flame
of gas burning in air, and below the flame of air burning
in gas.

159. Evaporation. — From e very-day life we can derive the
following qualitative information about the evaporation of
water:

1. It is rapidly converted into steam at 100°. When the
water has begun to boil all the heat offered is consumed in
changing the liquid to steam, so that the temperature remains
at 100® until the change is complete.

Fig. 47.— Flame of air
burning in hydrogen.

2. This change.

Water (liquid)

Water (vapor),

takes place slowly at lower temperatures. Countless facts,
such as the drying of sprinkled roads and washed clothing, give
evidence of this. The fact that wet garments can be dried out
of doors in cold weather, when the moisture they contain is

WATER AND HYDROGfcN 125

frozen, is a proof that water vapor escapes continually from
ice as well as from liquid water.

3. It follows from (2) that the air must contain water vapor.
The dew which forms on the outside of the ice pitcher confirms
this and illustrates condensation by cooling. The frost tracery
which forms on windowpanes shows that water vapor may con-
dense to ice, without passing through the liquid stage.

Since three-fourths of the earth's surface is covered with
water, we shall not be surprised at the fact that the air, on an
average, is two-thirds saturated with water vapor. We should
not allow the word "saturated" to lead us into the error that
the air soaks up water after the manner of a cloth or a sponge.
The water vapor is in exactly the same condition as the other
atmospheric gases. It occupies a share of the volume and
exerts a share of the pressure. Since it has a lower specific
gravity than nitrogen or oxygen, damp air is lighter than dry
air.

Definitions

Distillation. The purification of a liquid by boiling it and con-
densing the vapor.

Calorie, The unit of heat. The quantity of heat which will
warm one gram of water from 15** to 16**.

Reversible. A term applied to a chemical change which can be
driven either forward or backward by changing the concentrations
of the interacting substances.

Flame, Combustion in which the burning substance is a gas,
or is converted into a gas in the flame.

Evaporation. The escape of vapor from liquids below the boil-
ing-point.

CHAPTER X

SOME IMPORTANT OXIDES FOUND IN NATURE: TIN

DIOXIDE, ALUMINIUM OXIDE, MANGANESE

DIOXIDE, SILICON DIOXIDE.— THERMO-

CHEMISTRY

i6o. Tinstone. — Tinstone is the name given by miners to
a mineral which occurs in Bolivia, in Cornwall, England, in
the Malay Peninsula and some of the neighboring islands,
and in the Black Hills (S. Dakota). Its color is usually
brown. Often it is found without distinct crystallization,
in veins, or in pebbles along the beds of streams. The latter
can at once be distinguished from ordinary stones by their
high specific gravity (7).

i6i. Composition of Tinstone. — ^When pure powdered
tinstone is heated strongly in hydrogen in the apparatus of
Fig. 44 water is formed and tin remains in the bulb. Tin-
stone is therefore an oxide of tin. Quantitative work shows
that the atomic weight of tin (119 grams) is in combination
with 32 grams (two atomic weights) of oxygen. The sym-
bol of tin is Sn, from the Latin word stannum. The formula
of tinstone must be Sn02 and the chemical name, tin dioxide.
The name stannic oxide is also used, to distinguish it from
another oxide which has the formula SnO and is called
stannous oxide.

162. Action of Carbon on Tinstone. — ^When a mixture of
powdered tinstone with charcoal is heated in a hard-glass
test tube with a delivery tube dipping into limewater, the
latter becomes turbid. Melted tin remains in the test tube.

Sn02 + C — >■ CO2 + Sn.

Carbon acts in the same way upon many other oxides. The
removal of oxygen from an oxygen compound is called re-
duction. Tin dioxide is reduced by hydrogen and by carbon.

126

IMPORTANT OXIDES FOUND IN NATURE 127

The opposite of reduction, the addition of oxygen to a sub-
stance, is oxidation.

The formula of tin dioxide can be confirmed by oxidizing
a weighed quantity of pure tin foil in a porcelain crucible
and weighing the tin dioxide, which is identical with powder-
ed tinstone. 119 parts of tin combine with 32 parts of oxygen
by weight.

163. Tin. — Kn, the metal of tinstone, is a silver white
metal, with a brilliant luster. Its specific gravity is 7.3. It
is harder than lead, but softer than gold. At ordinary
temperatures it is malleable, and can be beaten into thin
sheets (tin foil). Tin foil is much used for wrapping food
products. At 100** tin is ductile; at 200*" it is brittle and can
be powdered in a mortar. It melts at 232 ** and boils at a
white heat. At very high temperatures, tin bums with a
white flame, to form tin dioxide, and melted tin slowly
absorbs oxygen and gives the same product. In the cold,
tin is scarcely afiFected by air or water.

164. Gray Tin. — Gray tin is an allotropic modification,
which is formed when tin is kept at low temperatures for a
long time. It has the same relation to ordinary tin that
ar-sulphur has to ^sulphur. Ordinary tin is stable above
20**, gray tin below.

Gray tin is a loose powder of specific gravity 5.8. It is
attracted by the magnet. Tin stored in unheated buildings
in winter sometimes turns to gray tin and crumbles. The
tin organ pipes of churches are sometimes damaged in this
way. Fortunately, the change of ordinary to gray tin is
very slow. If it was rapid, objects made of tin would fall
to pieces as soon as the temperature fell below 20°. Gray
tin can be quickly converted into ordinary tin by the action
of heat, for instance by pouring warm water over it.

165. Tin Plate. — Tin plate is made by coating sheets of
soft steel with tin. The steel is cleaned and freed from rust,
and then dipped into melted tin. It is very difficult to pro-
duce a really continuous coating, free from little perfora-

128 AN INDUCTIVE CHEMISTRY

tions. Some important alloys of tin are mentioned in the
table on p. 35.

i66. Action of Tin upon the Body. — Tin compounds are
very poisonous to plants, but much less so to animals. Large
doses produce acute disturbances of digestion, which pass
away without permanent injury. Doses of a centigram a
day for eighteen months have been administered to cats,
without any bad effect.

167. Production. — More than 100,000 tons of tin are pro-
duced each year, of which the Malay Peninsula and the
neighboring islands furnish three-fourths; most of the re-
mainder comes from Bolivia. Extensive deposits of tin-
stone exist in South Africa. Little tin is obtained in the
United States.

168. Corundum. — ^The ruby and the sapphire are forms of
a mineral called corundum, colored red in the first case and
blue in the second by traces of impurities. The best rubies
come from Burma, near Mandalay, while sapphires are found
in various localities, for instance, near Helena, Montana.
Both gems are made artificially. Corundum is rather
common in the United States, especially in the South.
Emery is an impure form of it, colored black by magnetite.
Most of the uses of corundum depend upon its hardness.
Among minerals, it comes next to the diamond in this re-
spect. It is largely used as an abrasive for polishing and
grinding.

169. Composition of Corundum. — Conmdum is the oxide
of a metal called aluminium. The oxygen and the metal
are firmly united and there is no convenient way of separat-
ing them in the laboratory. It is easy, however, to prepare
artificial corundum by synthesis. The powdered aluminium
used for painting mail boxes forms a suitable material. A
heap of it is placed upon a piece of asbestos board, which is
laid upon an iron plate. The combustion is started with the
burner-flame. The metal bums with an intense white light.
The asbestos is usually perforated by the heat. A very high

IMPORTANT OXIDES FOUND IN NATURE 129

temperature (3000° or over) is attained, partly because the
product of combustion is a soiid and does not cany o£E any of
the heat. A white powder of aliiminiiim oxide is obtained,
identical m composition with pure corundum. A quantita-
tive experiment shows that its formula is AljOj.

170. Aluminium. — Aluminium is a grayish white lustrous
metal, which will take a high polish. In the cold it is almost
unaffected by the air. It has about the same specific gravity

Fio. 4g.— MHUUfHcture of dumimum.

{2 . 6) -as glass, and is much lighter, therefore, than the other
familiar metals. It melts readily (660°). No satisfactory
solder for it has been found and pieces are united by welding.

171. Manufacture of Aluminium. — About 25,000 tons of
aluminium are made each year, and the production is in-
creasing rapidly. The manufacture rests upon the fact that
aluminium oxide, when dissolved in a suitable liquid, is de-
composed by the electric current, the aluminium separating
at the negative pole, the oxygen at the positive.

The liquid which has been found best for this purpose is
the melted mineral cryolite. Cryolite is found abun-
dantly in Greenland, It melts readily and dissolves alumin-
ium oxide freely. The melted cryolite is contained in the
rectangular box shown in Fig. 48 which is about 5 ft. long,
3 ft. wide and 6 in. deep. The box is lined with carbon and
is connected with the negative pole of the dynamo. The car-
bon rods shown in the figure form the positive pole. They
are connected with the box by a circuit in which is an incan-

130 AN INDUCTIVE CHEMISTRY

descent lamp (shunt), so that the current can pass either
through the lamp or through the liquid in the box.

When there is plenty of aluminium oxide in the bath, the
current passes mainly through the liquid because it offers less
resistance than does the lamp. But when the aluminium
oxide is nearly all decomposed, the resistance of the bath rises
and the current finds an easier way through the lamp, which
lights up. Then the workman in charge shovels more alu-
minium oxide into the bath, which is covered with a layer of
powdered coal to protect the eyes from the strong light of the
red-hot liquid. The aluminium collects beneath the melted
cryohte and is withdrawn from time to time. The oxygen
combines with the carbon of the rods and escapes as carbon
dioxide. The cryolite remains imaltered. Great care is
taken to use pure materials, for aluminium cannot be pmified
commercially. The aluminium oxide for this process is
prepared from batLodte, a mineral which contains chiefly
aluminium oxide and water. Bauxite occurs in France and
in the southern United States.

172. Uses of Aluminium: Occurrence. — On accoimt of its
lightness and strength, aluminium is used in making cameras,
opera glasses, drinking cups and soldiers' canteens. It
fcids application in automobile construction. The pure
metal makes excellent cooking utensils. These must not
be cleaned with soda or ammonia, both of which dissolve
aluminium. Aluminium foil is cheaper than tin foil and may
be used, instead of the latter, for wrapping food products.
The powdered metal, mixed with oil, is applied as a paint to
metallic surfaces. Small quantities of aluminium, less than
0.1%, added to melted steel just before it is cast, cause the
formation of dense, strong castings free from blowholes.
Cables and wires of aluminium are used to conduct the elec-
tric current.

Aluminium bronze contains 5 to 12% of aluminium, the
rest being copper. It has about the color and luster of gold
and is very strong. An alloy of aluminium with small

IMPORTANT OXIDES FOUND IN NATURE 131

quantities of magnesium is called magnalium. It is used for
the scales on instruments and for the beams of balances.
These alloys are more easily worked than pure aliuninium,
which sticks to the tools.

Aluminium does not occur in the free state, but its com-
pounds, clay and felspar for example, are among the most
common minerals. In point of abundance, it is third among
the elements, making up nearly 8% of the earth's crust.

173. Historical. — Prior to 1827, chemists had suspected for years
that corundum was the oxide of an unknown metal. In that year
Wohler confirmed this suspicion by preparing aluminium. About 1850
Sainte Claire-Deville obtained it in larger quantities and, at the Paris
Exposition, exhibited a bar of it labeled "L^argent de Fargile" — ^the
silver from clay. The electric process just described is the work of an
American chemist. Hall. It has reduced the price of the metal from
$90 a pound (1856) to about 20 cents at present.

174. Pyrolusite. — Pyrolusite is a black mineral, soft
enough to soil the fingers. It conducts the electric current
and is used as the material of the positive pole of one type
of cell, the negative pole being a rod of zinc and the liquid a
solution of sal-ammoniac. Such cells are used for ringing
door-bells and, very largely, for producing sparks in gas and
gasoline engines.

175. Composition. — Powdered pyrolusite is mixed with
granulated aluminium in a crucible, which is best lined with
magnesia. The crucible is set in a bed of sand and the mix-
ture heated at one point by burning a piece of magnesium
ribbon which has been thrust into it.^

A chemical change starts at the heated portion and spreads
through the mass, which becomes intensely hot (3000*).
When the crucible is cold, it contains two substances. The
upper layer is glassy and is easily identified as almninium
oxide by its extreme hardness. The lower is the metal of
pyrolusite, manganese, Pyrolusite is manganese dioxidej

^ This heating is best done by means of a cartridge supplied for the
purpose.

132 AN INDUCTIVE CHEMISTRY

Mn02, and the aluminium has taken the oxygen from the
manganese.

SMnOj + 4A1 — >■ 2AI2O8 + 3Mn.

176. Manganese. — Manganese^ is a hard, brittle, gray me-
tal whose luster is tinged with red. Its specific gravity is
8 and it melts above a white heat (1900°). It rusts in moist
air, and when the powdered metal is boiled with water,
hydrogen is set free, the manganese combining with the oxy-
gen. Compounds of the metal are widely distributed in
nature, being present m many minerals. Traces are found
in most soils and in the woody portions of some plants.
Tobacco, coflfee and tea do not grow well unless manganese is
present in the soil. Sea-water contains it, and great areas of
the deep sea floor are covered with round masses of pyro-
lusite.

177. Uses. — Manganese is used only in the form of alloys.
Its alloy with copper and zinc is manganese bronze, which is
very hard and strong. Manganese steel contains about 14%
of manganese. It was the pioneer of the special steels, which
have become so important of late years. Its toughness and
strength make it valuable for the jaws of stone-crushers
and for other objects which have to stand rough usage.

Since all iron ores contain manganese, the pig iron made
from them also contains it (up to 4%). Spiegeleisen is pig
iron containing 15-20% of manganese. The name, which
means mirror-iron, is due to the brilliant facets of the crystals,
which appear in the broken surfaces when a bar is fractured.
In ferrcMnanganese the manganese runs up to 80%, the bal-
ance being chiefly iron and carbon. Both these alloys are
widely used in steel making.

Manganese ores (pyrolusite and other oxides) are used in
great quantities in the manufacture of spiegeleisen and ferro-

^The similarity of the name of manganese to that of magnesium
often leads to confusion. The two are different elements, having
little resemblance to each other.

IMPORTANT OXIDES FOUND IN NATURE 133

manganese. The inost productive mines are in Brazil,
India and the Caucasus. Russia is the chief producer.

178. Quartz. — Quartz is the most common of minerals.
Twelve per cent of the earth's crust consists of it. Many of
the most abimdant rocks, like granite, gneiss, mica schist and
sandstone contain it.

. The shape of a typical quartz crystal is shown in Fig. 49.
A hexagonal prism is terminated at each end by a hexagonal
pyramid. Natural crystals have usually
grown fast to the rock at one end, which is
therefore not developed. Often they are
foimd in groups.

Clear colorless quartz is called rock crystal.
During the middle ages it was supposed to
be composed of water, which had been so
thoroughly frozen by intense cold, that it was
impossible to melt it. When cut and polished,
rock crystal makes the rhinestone or quartz
diamond. It can be distinguished at once
from the true diamond by its different luster
and inferior hardness. Clear quartz crystal, colored violet
by a Uttle manganese is the amethyst; colored yellow the
false topaz.

Quartz is also found in irregular masses composed of
microscopic crystals. It is then called chalcedonyy agate,
carnelian or onyx according to the color and other properties.
Petrified wood is produced when wood decays under water
containing dissolved quartz. The quartz replaces decaying
wood bit by bit, so that the structm-e of the wood is pre-
served. Flint is massive quartz which when struck with a
hammer, usually breaks into pieces with a sharp cutting
edge. It was used for knives and arrowheads by prehistoric
man. Quartz is the chief constituent of most ordinary
sand. Pure quartz in the form of clean, white sand, or of
rock crystal, is used in great quantities in the manufacture

of glass.

PiQ. 49. — ^A quarts
crystal.

134 AN INDUCTIVE CHEMISTRY

179. OpaL — Opal has nearly the same composition as
quartz, but is amorphous. It is also less pure, containing
water and usually ferric oxide as impurities. Infusorial
earth is a mass of minute shells consisting of opal. It is used
m scouring powders and for the manufacture of dynamite.
When opal exhibits a beautiful play of colors, it is used as a
gem. The finest stones come from Hungary, Mexico, Aus-
tralia and Honduras.

180. Silicon. — Quartz is an oxide and, when the powdered
mineral is heated with magnesium, there is a violent re-
action which may be explosive. The oxygen of the quartz
combines with the magnesium and the other element is ob-
tained as a brown powder. It is called silicon. Quartz is
silicon dioxidey Si02, and the equation is

SiOa + 2Mg — ^ Si + 2MgO.

Sand consists chiefly of roimded grains of quartz, and silicon
is now made on a large scale by heating a mixture of sand
with coke to the high temperature of the electric furnace.

Si02 + 2C — ^ Si + 2C0.

Silicon made in this way is a gray, lustrous crystalline mass,
harder than glass and nearly three times as dense as water.
Its chief use is in the manufacture of steel. Small quantities
of silicon added to the melted metal, just before poming into
the mould, cause the formation of dense, sound ingots. We
have noted the use of aluminium for the same purpose
(p. 130).

181. Silicon Monoxide. — ^When sand is heated in an elec-
tric furnace with an amount of coke only sufficient to remove
half the oxygen, silicon monoxide, SiO, is obtained. This
is a light yellowish brown powder which bears the commercial
name of monox. It is used as a paint.

182. Silicon CarbidCi SiC. — On the other hand, when more
coke is used than is needed to remove all the oxygen from
the sand, the liberated silicon unites at once with carbon and

IMPORTANT OXIDES FOUND IN NATURE 135

forms silicon carbide, SiC, which is called carborundum. In
practice some salt is added to the mixture of coke and sand
to make it melt more readily, and some sawdust to make it
porous. The reaction, howeverj is entirely between the
sand and the carbon.

SiO, + 3C — >■ SiC + 2C0.

The materials are contained in a rectangular furnace whose
sides are built of loosely piled bricks (Fig. 50). The carbon
electrodes project itato the mass through the end walls.
There is a core of
granulated coke im-
bedded in the mix-
ture, reaching from
one electrode to the
other. This, beii^ a

bad conductor, is in- Fio. so.— carborundum tiirasoB.

tensely heated when

the current b turned on. A powerful current passes lor eight
hours, during which time, the heat from the coke core pene-
trates the mass and the change indicated in the equation
above occurs. The current acts only as a source of heat.
The furnace is then allowed to cool and the side walls torn
down to remove the product.

Carborundum when pure is in colorless crystals, but usu-
ally it is brown or black. It is harder than ruby and almost
as hard as the diamond. It finds wide application as a sub-
stitute for emery in making hones, whetstones, grinding
wheels and polishii^ paper. It is also used for the crown,
or cutting edge, of rock drills.

The intense heat of the carborundum furnace converts the
coke of the core into artificial graphite (p. 43).

In the manufacture of carborundum the electric current serves merely
as a heating agent. A proceea of this kind in which the current is used
simply aa a means of obtaining a high temperature is called an eleclro-
titenrud process. In the carborundum furnace. Fig. SO, the high tern-

136

AN INDUCTIVE CHEMISTRY

FiQ. 61. — ^Diagram of furnace heated by an electric arc.

perature is produced by the passage of a heavy current through a bad
conductor against a high resistance. Fig. 50 will serve as an example
of the resistance type of electric furnace, in which an elevated tempera-
ture is produced by putting a badly conducting body of some kind into
the path of the current. We have seen that such furnaces are in ex-
tensive use.

The arc type of electric furnace is shown in Fig. 51. The arc is made
to bum between heavy carbon rods below which is placed the crucible

containing the sub-
stance to be heated.
The crucible and the
furnace-lining must
be made of some sub-
stance which is ex-
ceedingly refractory
(difficult to melt).
Furnaces in which
the high temperature of the arc (nearly 4000^) is utilized are coming
into wide use in the steel industry.

183. Silicon in Nature. — ^Although silicon does not occur
in the free state, its compounds are so common that it comes
next to oxygen in point of abundance, making up 28% of the
earth's crust. Feldspar, mica, hornblende, and most of the
other rock-forming minerals, contain it. Limestone is the
only common rock which is not made up of silicon compounds.
It plays, in the mineral world, somewhat the same part that
carbon does in organic nature. All river, well and spring
waters contain small quantities of dissolved silicon com-
poimds.

Silicon dioxide is called silica. It is now made into crucibles, dishes
and thermometers for the laboratory. Such ware is made by melting
pure quartz with a flame of illuminating gas fed with oxygen. It is
expensive, but has the merit of never cracking when suddenly heated
or cooled. The stems of many plants, like rye, wheat, grass and bam-
boo, are rich in silica. It is also contained in sponges and in the quills
of feathers.

184. Thermite. — ^We have noted the preparation of man-
ganese from a mixture of manganese dioxide and alumin-
ium. When a mixture of ferric oxide with one-third of its

THERMOCHEMISTRY 137

weight of granulated aluminium is strongly heated at one
point, the reaction

FesO, + 2A1 — >■ AI2O3 + 2Fe

begins at the heated portion and spreads through the mass,
which is carried to a temperature of 3000*".

The mixture is sold under the name of thermite. It is
useful, not for the manufacture of iron, which can be made
far more cheaply by other methods, but for the production
of high temperatiu'es. Trolley rails and iron pipes are
welded by means of it and broken shafts on steamships are
repaired without removal.

185. Chemical Energy. — Energy, especially in the form
of heat, is usually produced during chemical changes. The
use made of thermite shows that, in that instance, this
energy is much more important, from a piu'ely practical
standpoint, than the material products of the reaction.
This is very often the case. Many chemical changes are
carried out entirely for the yield of energy, the substances
produced being discarded. The use of fuel is a striking
example. We bum coal, wood, oil or candles to get energy
as light or heat and the substances (carbon dioxide and
water) which are formed at the same time are simply allowed
to escape. Explosives are employed purely for the energy
which they yield. Magnesium powder is burned in photo-
graphic flash-lights solely for the light energy, and the mag-
nesium oxide produced is merely a nuisance. In the electric
batteries which nm our door-bells, telegraph instruments
and explosion engines, we consume zinc purely to produce
electrical energy, and the zinc compounds which result are
discarded.

186. The Measurement of Energy as Heat. — Chemical
energy is measiu'ed in the form of heat The reason for this
is that it is easy to carry out a chemical change in such a
way that all the energy which is given out takes the form of
heat, while it is impossible to obtain aU of it in any other

138 AN INDUCTIVE CHEMISTRY

form. The unit of heat energy is the amount required to
warm one gram of water through one degree centigrade.
Practically, therefore, we carry out the chemical process,
whose energy is to be measured, in a vessel which is immersed
in a second larger vessel containing a known weight of
water. From the rise in temperature of the water in the
outer vessel, the energy yield of the chemical change which
has occurred in the inner vessel is determined.

Thus, when cuprous sulphide is formed from copper and sul-
phur, much heat is evolved. The quantitative statement is

2Cu + S — ^ CU2S + 20,000 calories.

This means that, when two atomic weights (127 grams) of
copper unite with one atomic weight (32 grams) of sulphur,
enough heat is produced to raise the temperature of 20,000
grams of water 1°C. This is nearly the same as the heat re-
quired to raise 200 grams of water from the freezing- to the boil-
ing-point. 20,000 calories is the heat of formation of cuprous sul-
phide; that is, it is the heat given out when a molecular weight
of it (159 grams) is formed from 127 grams of copper and 32
grams of sulphur.

In order to break up a molecular weight (159 grams) of cuprous
sulphide into copper and sulphur, the 20,000 calories which
escaped when it was formed must he supplied. For otherwise we
could create out of nothing any desired amount of energy by
simply combining copper and sulphur (obtaining 20,000 calories)
and then separating the cuprous sulphide.

187. Thermochemical Equations. — An expression Hke that
given above, which takes account of the energy side, as well as
the matter-side, of a chemical change, is called a thermochemi-
cal equation. Here are some additional examples:

(1) C + O2 — >• COi + 100,000 cal.

(2) H, -f O — >■ H2O + 70,000 cal.

(3) 2A1 + 30 — >- AI2O, + 380,000 cal.

(4) 2Fe + 30 >- FeaQ + 196,000 cal.

The large amounts of heat produced when carbon and hydrogen
unite with oxygen (1 and 2) explain the universal use of sub-

THERMOCHEMISTRY 139

stances containing these two elements for fuel. The enormous
heat of formation of aluminium oxide (3) accounts for the uses
of thermite. But only about half of the 380,000 cal. is avail-
able when thermite is used. The equation

Fe,0, + 2A1 — >- A1,0, + 2Fe

shows that ferric oxide is separated at the same time that alu-
minium oxide is formed, and the 196,000 cal. required for this
must be subtracted to get the actual amount of heat produced,
which is

380,000 — 196,000 = 184,000 cal.

for each molecular weight of aluminium oxide formed (102
grams).

An exothermic chenlical change is one which produces heat.
The formation of the four oxides just mentioned will serve as
examples.

We have seen that, in decomposing mercuric oxide into its
elements, a continuous supply of heat is required. The ther-
mochemical equation explains this fact:

HgO — >- Eg + O - 21,500 cal.

An endothermic change is one, which, like the decomposition
of mercuric oxide, absorbs heat.

Definitions

Reduction, The removal of oxygen from an oxide.

Oxidation. The addition of oxygen to a substance.

Stable, Showing httle tendency to change. Thus, water is a
stable compound. Nitroglycerine is unstable.

Heat of formation. The heat given out when a molecular weight,
in grams, of a compound is formed from its elements.

CHAPTER XI

THE ACTION OF OXYGEN ON SULPHIDES AND OF

CARBON ON OXIDES.— METALLURGY OF ZINC,

LEAD, MERCURY, TIN AND IRON.—

WATER GAS

i88. The "Roasting" of Sulphides. — The great quantities
of sulphur dioxide which are needed for the manufacture of
sulphuric acid are made from pyrite. When the mineral is
heated in a current of air, it bums with a blue flame: sulphur
dioxide escapes and ferric oxide remains.

2FeS2 + 110 — >- FeaOs + 4S02.

The sulphides of the other common metals behave in the
same way; sulphur dioxide escapes and the oxide of the
metal is left.

(1) ZnS + 30 — ^ ZnO + SO,

(2) PbS + 30 — ^ PbO + SOa

The first stage in the extraction of zinc from zinc blende is
to convert the sulphide into zinc oxide in this way (1). The
process is called "roasting." It can be carried out in a

re verberatory furnace

(Fig. 52). The fuel bums
at one end and the com-
bustion products traverse
the whole length of the
furnace before they es-
cape from the flue at the
other. The roof is low,
so that the heat is re-

FiG. 52. — ^A reverberatoiy furnace.

fleeted down upon the charge, which is placed upon the
bed of the furnace.

In order to extract the lead from lead-glance^ it is first
roasted to oxide in a reverberatory furnace. About 10% of

140

ACTION OF OXYGEN ON SULPHIDES 141

lime is mixed with the lead-glance. In some way, at present
unexplained, the lime greatly facilitates the change of the
lead sulphide into lead oxide. In order to avoid meltmg the
ore, or vaporiaing the lead oxide, the temperature is carefully
regulated. The lead oxide, like the zinc oxide, is afterward
heated with carbon (coke or coal) to obtain the metal.

189. Roasting of Cinnabar. — When cinnabar is roasted,
sulphur dioxide escapes, but mercuric oxide cannot be
formed, because it is decomposed by heat. Therefove the
chemical change takes the course indicated by the equation

HgS + Os —^ Hg + SO,.
The mercury is swept along as vapor in the stream of furnace
gases and its condensation is the chief difficulty.

Fig. 53 is a dJEigrara of the furnace and a portion of the condenBing
apparatus. The rectangular shaft A is surrounded by an iron jacket
and built upon an
iron plate to prevent
leakage of mercury.
The miicture of lump§
of ore with charcoal
is placed in the cup-
ehsped space at the
top, and when the
cone is bwered, the
mixture slides into
the furnace. A Kd c,
which is like an in-
verted basin with its
edges dippii^ into
water, prevents the
escape of mercury
vapor. Through d,
the fire gases carry- Flo.Sa.-FurnMeforroBfltingomnabiirinaourrenlof air.

ing the mercury va-
por are led through condensing arrangement, which consists of a
number of Q-shaped earthenware pipes. These pipes open at the
bottom into acovered cement trough, partly full of water, in which
the mercury collects. The gases then pass through long under-
ground wooden passages and atone chambers to complete the

142 AN INDUCTIVE CHEMISTRY

In spite of all this care, about ^ of the mercury in the ore ie lost, and
the workmen suffer from mercuiial poisoning.

190. Action of Carbon on Oxides. — The oxides which oc-
cur native, like those of tin and iron, as well as those that are
made from the sulphides, hke zinc oxide and lead oxide, are
converted into metal by heating them with carbon (charcoal,
coal or coke).

Tin oxide is mixed with anthracite coal and heated on the
bed of a reverberatory furnace (Fig. 52).

SnOj + C — ^ Sn + CO,.

The tin is tapped off through a hole not shown in the dia-
gram.

Lead oxide, mixed with coke, is charged in at the top of a
small cylindrical blast furnace often 6 meters high and 1

Fio. 54. — Fumue for the reductiDn of lina oiide witb caiboa.

meter in diameter. Through tubes which project into the
furnace near the bottom a blast is introduced. The equa-
tion is

2PbO + C — >- 2Pb + CO,.

The lead is tapped off below from time to time.

Zinc oxide, mixed with coke, is placed in a retort, O-shaped
in cross section, often 2 m. long and 50 cm. high (m, Fig. 54).
These retorts are heated from the outside; the fuel which does

METALLURGY

143

the heating is separate from that which causes the reduction
of the. zinc oxide.

ZnO + C — >■ Zn + CO.

F is a fire-clay receiver in which most of the zinc condenses.
In the sheet-iron tube a, some of the zinc, which escapes con-
densation in Vy collects as a gray powder called zinc dust,
which goes back into the retort m with the next charge.

The first portions of this zinc dust which collect contain the cadmium
which is often present as an impurity in zinc blende. Cadmium is a
tough, soft, white metal, denser than zinc, which it resembles in chemical
properties. It is used in the manufacture of fusible alloys. Cadmium
oxide, CdO, is a brown powder. The sulphide, CdS, is employed as a
paint under the name "cadmiiun yellow.''

Related Topics

191. Metallurgy of Iron. — The most important ores of iron
are oxides of the metal. Their reduction is carried out in a
large round blast furnace (Fig. 55),
80-100 ft. high and 20-25 ft. in
diameter at the widest part, which is
below the middle. Such a furnace
will produce up to 2500 tons of iron
a week, consuming about an equal
weight of coke and about three times
the quantity of iron ore. It is built
of fire brick, strengthened by iron
bands.

The blast enters through 8-10 noz-
zles, called tuyheSf which are set
around the furnace near the bottom.
The tuyeres are made double and are
cooled by water circulating in the
interior, for the blast has a tempera-
ture of 800° (dark red heat). The
coke burns at first to carbon dioxide,

which is at once converted into carbon monoxide by the
glowing fuel through which it rises on its way to the top of
the furnace:

CO2 + C — >• 2C0.

Fia. 65. — Blast furnace for the
reduction of iron ore.

144 AN INDUCTIVE CHEMISTRY

The carbon monoxide removes the oxygen from the iron ore :
FejOs + 300 -"^ 2Fe + SCO,.

This reaction, as the arrows indicate, is reversible. In order
to drive it from left to right, reducing iron oxide, the concen-
tration of the carbon monoxide must be at least twice as great as
that of the carbon dioxide. The important practical result of
this is that no further reduction of iron oxide takes place in the
blast furnace after the carbon monoxide in the gases is so far
consumed that its percentage by volume has dropped to about
twenty, the carbon dioxide at the same time having risen to
about ten per cent. Even if the gases were forced through a
second column of glowing iron oxide in another furnace, there
would be no effect. Equilibrium has been reached.

Before this was understood, it was thought that the reason
the gases still contained so much carbon monoxide, after pass-
ing through the furnace, was that the column of iron ore was
not long enough to extract all the carbon monoxide and expen-
sive attempts to utilize the fuel more completely by building
higher furnaces were made, entirely without success.

At present, the gases are led from the top of the furnace, by a
large pipe called the "down-comer," to the blast stove. This
is a structure of fire brick and iron, about half the height of the
furnace. The interior is of fire brick, arranged so as to offer a
large surface to gases passing through it. In this arrangement
the 20 % of carbon monoxide which the gas contains is burned
by the admission of air and the fire brick interior of the blast
stove is heated bright red. Then the direction of the current
of gas is changed, so that the air goes through the hot blast
stove on its way to the tuyeres, and by contact with the red-hot
fire brick is strongly heated before it enters the furnace. Mean-
while, the gas from the "down-comer*' goes into another blast
stove, which is being heated. To provide for cleaning and
repairs, three or four blast stoves are needed for each furnace.

192. Slag. — The reduced iron in the upper part of the furnace
is finely divided. As it sinks into the hot zone near the tuyeres,
it melts, and the liquid collects in the bottom, from which it is
removed by tapping every four hours. The tap hole is then
closed with moist clay which immediately bakes into a hard
plug. Above this tap hole, is the slag hole, through which the

METALLURGY 145

slag is allowed to flow into tubs, which, when full, are taken to the
dump. This slag is a glassy substance, which is liquid at the
temperature of the furnace. It is composed of the clayey im-
purities of the ore (silica and aluminium oxide) together with the
hme of limestone, which is added systematically with the charge
through the cup and cone at the top, to assist slag formation.
One important function of the slag is to cover up the liquid iron,
so that it shall not be burned into oxide by the blast from the
tuyeres.

About a ton of slag is formed for each ton of iron. Some of
it is used for road mending, roofing material and considerable
quantities for cement, but the utilization of the enormous
amounts which are produced is an unsolved problem.

193. Cast Iron. — Sometimes the liquid iron is run into de-
pressions in a bed of sand in front of the blast furnace, where it
freezes to bars of crude iron called pigs. Cast iron is brittle and
cannot be welded or forged. Ranges, stoves, pipes, radiators
and all the objects which are cast in ordinary foundry work are
made of it. It is unsuitable for an3rthing which is to be exposed
to shock or great strain.

Cast iron is the most impure variety. It contains:

(1) Carbon (3 to 4%) derived from the coke.

(2) Silicon (up to 2%) derived from the silica of the ore.

(3) Manganese^ a variable quantity, depending upon the ore.
By using pyrolusite along with the iron ore in the blast fur-
nace, the manganese in the pig can be run up to 20% (spiegeleisen)
or even to 80% (ferromanganese). The wide use of these alloys
in making steel depends upon the fact that they are rich, not
only in manganese, but also in carbon.

(4) Sulphury derived from the ore and the coke. This is a
harmful impurity in both iron and steel, making them brittle
when hot ("red short")- 0.1% makes a steel rail roll badly and
very much smaller quantities are objectionable in the better
grade steels which are used for railway bridges, boiler plates,
ship armor, etc.

(5) PhosphoriLSf familiar from its use in making matches.
It makes iron and steel brittle when cold ("cold short"). 0.1%
would be rather dangerous in a rail and 0.025% is enough to
spoil cutlery steel. In cast iron, its bad effect is less marked.

146 AN INDUCTIVE CHEMISTRY

194. Wrought Iron. — Wrought iron is the purest commercial
form of the metal. It is made by melting pig iron in a rever-
beratory furnace (Fig. 52) in contact with a layer of iron oxide.
The five elements just mentioned combine with the oxygen of
the iron oxide. Carbon dioxide and sulphur dioxide escape
as gases; the oxides of silicon, manganese and phosphorus enter
the slag. When the metal is nearly pure, it becomes semi-
solid. It is then formed into balls about 80 lbs. each in weight,
which are placed under a steam hammer to squeeze out the slag,
and then rolled into bars. The whole operation takes about an
hour and a half. The carbon can be reduced from say 4% to
0.1%; the other impurities are almost completely removed.

Wrought iron melts at a much higher temperature than cast
iron. It is much tougher and can be forged and welded. It is
used for rails, chains, bolts, wire, horseshoes and similar objects.

195. Steel. — Cast iron contains an average of 4% of carbon,
wrought iron very little (about 0.1%). Steel is intermediate.
Razor and file steel contain about 1 . 5%, tool-steel 1 . 25%,
while 0.75% of carbon or less gives a soft, "mild" steel which
will not hold a cutting edge. Evidently, if cast iron and wrought
iron were melted together, the product would be steel, for the
percentage of carbon would have an intermediate value. Cruci-
ble steel, which is the highest grade of steel, is still largely made
by melting pure cast iron with wrought iron, or wrought iron
with charcoal, in crucibles made of a mixture of graphite and
fire-clay. A little ferro-manganese is added towards the end of
the process. This causes the steel to be free from blowholes.
The crucibles last only for three heats, and are being rapidly
displaced by electric furnaces.

Crucible steel is expensive, and is used only for small objects
in which quality is the first consideration. Watch springs,
needles, pens, tools, razors and other cutlery are made of it.

196. Temper. — When crucible steel is heated red-hot, and
then quenched in water, it becomes as hard as glass. If then
re-heated, and allowed to cool slowly, it is softened to an extent
depending upon the temperature of the second heating. This
is called "drawing the temper.'' Thus if re-heated to 230°, the
steel is still very hard and is suitable for razors and surgical
instruments. Re-heating to 270° gives a somewhat softer, less

METALLURGY

147

Fia. 56. — Converter.

brittle steel, useful for axe heads. The importance of this
process, in fitting the steel for various purposes, is plain.

197. Bessemer Steel. — The great quantities of cheap steel
used for girders, highway bridges and rails are, in part, made by
the Bessemer process. Melted cast iron is taken from the blast
furnace in a great ladle

and poured into the con-
verter (Fig. 56), which is
a pear-shaped vessel,
often 15 ft. high by 8 ft.
in diameter, made of
steel, lined with bricks
rich in silica (SiOa).
Here a blast is forced
through the liquid metal
from fire clay tuyeres
in the bottom. The sili-
con and manganese are
oxidized first and pass
into the slag. Then the

carbon oxidizes, and escapes as carbon monoxide, which bums
to carbon dioxide with a bright flame at the mouth of the
converter. The sulphur and phosphorus are not affected. When
the removal of the carbon is complete, enough melted
spiegeleisen is added to put the desired quantity of carbon
and manganese into the steel, which is then cast.

Since phosphorus is not removed in the ordinary Bessemer
process, it is necessary to use iron almost free from this unde-
sirable element. If, however, the converter is lined with a
mixture of magnesium oxide and lime, the phosphorus unites
with these materials, leaves the metal and passes into the slag.
Good steel can thus be made from iron rich in phosphorus.
This important modification is called the Basic Bessemer proc-
ess. It is largely used in Europe, but not in this country, be-
cause the ores are not suitable. On account of the phosphorus
which it contains, the slag of the basic process forms a valuable
fertilizer.

198. Open Hearth Steel. — The open hearth process^ by which
large and increasing quantities of steel are being made, is, from

148 AN INDUCTIVE CHEMISTRY

a chemical point of view, similar to the manufacture of wrought
iron (p. 146). Melted iron is taken from the blast furnace to
the hearth of a great reverberatory furnace, where it ia heated
with iron oxide (iron ore) until moat of the carbon, eihcon,
manganese, phosphorus and sulphur are removed by oxidation.
Thia requires twelve hours or more. Then enough apiegel or
ferro-mangaoese is added to introduce the desired amount of
carbon. The manganese prevents blowholes and gives a sound
casting.

A diagram of the furnace is pven in Fig. 57. The regenera-
tive By$tem of heating should be noted. The gas, which is used

FiQ. ST. — Regeoerativs fiuoaoa for the open-heoxth prooeaB.

as fuel, passes through a checkerwork of red-hot fire brick on its
way to the furnace. The air, before it enters the furnace, is
heated in the same way. Thus, a higher temperature is ob-
tained in the furnace than could be produced by the use of cold
gas and cold air.

On their way out of the furnace, the products of combustion
pass through two exactly similar checkerworks, which in about
half an hour, are heated to a bright red heat. Then the direc-
tion of the gas and air is reversed. The cold gas and air on
their way to the furnace pass through the heated checkerworks,
the gas through one and the air through the other, while the

WATER GAS 149

other two systems are now heated by the hot gases from the
furnace.

An open hearth furnace may hold fifty tons or more of melted
metal. In order to utilize it, scrap steel is often added with the
iron. The advantage of open hearth over Bessemer steel is
that the process is under better control. The metal can be
kept liquid on the hearth for hours; samples can be withdrawn
and tested and additions of more pig iron or spiegel made if
necessary. All this is impossible in the Bessemer converter,
where the whole conversion is effected in twenty minutes and
the metal freezes if there is any delay.

This means a large consumption of fuel and, accordingly,
open hearth steel is a more expensive product than Bessemer
steel, and is used for armor plate, heavy guns, machinery, boiler
plates, railway bridges and so on. Many rails are now being
made of open hearth steel and its use for this purpose is likely
to become general. Increased speed and increased weight of
both locomotive and cars have made it necessary to lay a
tougher rail.

199. Water Gas. — Red-hot carbon acts upon steam as it
does upon other oxides.

H2O + C — >- CO + H, - 28,300 cal.

In a steel cylinder lined with fire brick (Fig. 58) a fire of an-
thracite or coke is raised to a white heat by a blast of air in-
troduced below the grate. This takes about ten minutes.
Then the air is shut off and steam injected below the grate.
The above equation shows that the resulting gas would contain,
if pure, 50% by volume of carbon monoxide and 50% by volume
of hydrogen. In practice, it also contains some carbon dioxide
and nitrogen. The thermochemical symbols show that the
reaction absorbs much heat. Hence the injection of the
steam can only be continued five minutes, when the fuel-
bed becomes cooled to such an extent that the interaction no
longer occurs satisfactorily. Then the steam is stopped and the
air blast restored.

The product is called water gas. It bums with a blue flame.
In order to make the flame luminous, it is passed downward
through a second cylinder called the "carburetter" (Fig. 58) in
11

160 AN INDUCTIVE CHEMISTRY

which it cornea into contact with a spray of petroleum, and then
upward though a tliird cylinder called the "superheater," which
is packed with a checkerwork of red-hot fire brick. In the super-
heater the vapor of the petroleum ie converted into gases which
cause the water gas to burn with a luminous flame. The
illuminating gas of the large cities of the United States is largely
made in this way. How-
ever, at present the de-
velopmentof mantle-light-
ing has made the light-
giving quality of the gas
flame unimportant. It is
the heat value of the gas
which counts at present,
for the gas which Uberates
the largest number of
calories when it bums will
i heat the mantle to the
b highest temperature, and
2 BO produce the most
"s light.

I 300. Producer Gas, —
I Interrupting the produc-
I tion of gas every five
I minutes, in order to heat •
P up the fuel bed, can be
^ avoided by admitting a
^ certain amount of air vnth
^ the steam. The air burns
some of the fuel to carbon
monoxide:

C+O >-CO+29,300cal.,

and the heat liberated
compensates for the cool-
ing effect of the reaction
between the carbon and
the steam.

This is the way in which
the great quantities olfvel

WATER GAS 151

gas used about steel works and similar places are made. Such
a gas will contain by volume, about

30% carbon monoxide
15% hydrogen
5% carbon dioxide
50% ntrogen

The jet of steam is made to suck in the required quantity of air,
on the principle of the Bunsen burner. The gas is easily and
cheaply made from coke, anthracite, or even bituminous coal,
and has a high heat value.

BOOK III

THE ATOMIC THEORY.— IMPORTANT COMPOUNDS

CONTAINING HYDROGEN

INTRODUCTION

We have seen that the kinetic theory, which explains the
properties of gases by the assumption that they consist of
molecules in rapid motion, has practically become a fact,
owing to the irresistible evidence recently brought to its sup-
port. We must now enquire whether the molecule is a
simple, indivisible mass, or whether it is a structurej composed
of smaller particles. This question will be investigated in
Chap. XII. Chap. XIII will be devoted to the com-
pounds which hydrogen forms with sulphur and with ni-
trogen, and Chap. XIV to a few of the compounds of car-
bon and hydrogen, of which more than two hundred are
known at present. In Chap. XV we shall study a class
of compounds containing carbon, hydrogen and oxygen,
which are abundant in nature and of great practical impor-
tance.

153

CHAPTER XII
THE ATOMIC THEORY

201, Atoms. — Carbon dioxide is composed of molecules,
all of which are exactly alike. If, then, we could catch a
single molecule, and analyze it, it would contain the same
proportions of carbon and oxygen which are found in measur-
able quantities of the gas, that is, 12 parts of carbon and 32
parts of oxygen by weight. A molecule of carbon dioxide is
not a simple particle, but a group of smaller particles which
move about without parting company, and these smaller
masses of which the molecule consists are of two kinds, par-
ticles of carbon and particles of oxygen.

The same statement is clearly true of all gases which are
chemical compounds, Uke carbon monoxide, sulphur dioxide
and steam. Their molecules must be composed of groups of
particles of the elements of which they consist. But most
solids and liquids can be converted into gases, by applying
the proper temperature and pressure. Therefore, we can
make a general statement that the molecules of all chemical
compounds must consist of groups of smaller particles of the
corresponding elements. To these smaller particles the name
atoms is given. Atoms are the constituents of molecules.
There are as many kinds of atoms as there are elements, that
is, about eighty.

202. Value of the Atomic Theory. — The atomic theory
gives a clear and simple account of the laws of chemical
change, which we have hitherto regarded purely as facts.

The most fundamental fact in our science is, that there are
such things as atomic weights^ that is, that there is^ for each
element J a number of parts by weight in which it is present in all
of its compounds. By means of these numbers, and small
multiples of them, the composition of all chemical compoimds
can be expressed.

154

THE ATOMIC THEORY 155

According to the atomic theory, these numbers are the
relative weights of the atoms. Thus the atom of carbon
weighs three-fourths as much as the oxygen atom. If, as the
basis of our system, we take the arbitrary number 16 for
the atomic weight of oxygen, the atomic weight of carbon be-
comes 16 X M or 12. Carbon monoxide contains 12 parts of
carbon to 16 of oxygen by weight. Its molecule, then, con-
tains one atom of carbon (weighing 12) and one atom of
oxygen (weighing 16). Since every atom of carbon weighs
12 and every atom of oxygen weighs 16 the proportions of
carbon and oxygen in every molecule of carbon monoxide will
be the same. Any measurable quantity of carbon monoxide
is simply a very large number of such molecules and its com-
position will be the same as that of a single molecule. Hence
the law of definite proportions; that the composition of a
compound is constant. The same compound always con-
tains the same number of the same kind of atoms in its
molecule. Since each of these atoms has a constant weight,
the composition of the molecule, and therefore of the com-
pound, must be constant

203. Multiple Proportions. — Carbon dioxide contains 12
parts of carbon to 32 of oxygen and has the formula CO2. It
contains twice as much oxygen, for the same weight of car-
bon, as the monoxide. This is an instance of multiple pro-
portions. When carbon monoxide bums, the carbon atom,
which is already combined with one oxygen atom, takes on
another. No less than a complete additional atom can be
added, because the atoms are not divisible (from ^'ato/Ao?j in-
divisible)

204. Compounds of Sulphur and Oxygen. — Study of many
sulphur compounds shows that the atomic weight of sulphur
is twice as great as that of oxygen: hence if we assign the
number 16 to the latter, sulphur assumes the value 32. The
synthesis of sulphur dioxide (p. 94) shows that it contains
equal weights of its two elements; hence the formula must be
SO2. A molecule must contain one atom of sulphur united

156 AN INDUCTIVE CHEMISTRY

with two of oxygen. Sulphur trioxide, which contains 48
parts of oxygen united with 32 of sulphur, receives' the for-
mula SOa. Its molecule contains four atoms, one of sulphur
and three of oxygen.

The symbols, which we have been using to denote the
chemical unit quantities of the elements, can be read as
meaning atoms of the elements. The symbol S may be used
to mean 32 grams of sulphur, or as meaning an atom of sul-
phur which weighs 32, if the atom of oxygen weighs 16.

We have been using the formulas of compounds to denote
weights of them which are produced by the union of the
chemical unit weights of the elements. In the case of gases
we have noted the surprising fact (p. 110) that the weights
represented by the formulas of the different compounds fill
the same volume under the same temperature and pressure
(22.4 liters at S.T.P.).

The formula can just as well be used to indicate a molecule
of the compound. Thus SO2 may be used to mean (a) 32
grams of sulphur united with 32 grams of oxygen to form 64
grams of sulphur dioxide, which fill a volume of 22.4 liters
at S.T.P.; or, it may mean (b) a group of three atoms, one
of sulphur and two of oxygen, combined to form a molecule of
sulphur dioxide. These two meanings are not so different as
might at first sight be supposed. The numbers (atomic
weights) remain the same and so, therefore, do the relative
quantities in which the elements are present. Since actual
chemical work is always done with weighable quantities, (a)
is usually the more important meaning to bear in mirid. The
student will now perceive the reason for the use of the terms
atomic and molecidar weight. The abbreviation mole is em-
ployed for the molecular weight in grams. Thus:

64 grams is a mole of sulphm* dioxide, SO2.
44 grams is a mole of carbon dioxide, CO2.
18 grams is a mole of water, H2O.
88 grams is a mole of iron sulphide, FeS.
216 grams is a mole of mercuric oxide, HgO.

THE ATOMIC THEORY 157

We have seen (p. 110) that the volume of the mole is the
same for all gaseous compounds, 22.4 Uters at S.T.P. In
fact, if we were investigating a new gas, whose chemical com-
position was entirely unknown, we could nevertheless deter-
mine its molecular weight by getting the weight of 22.4 Uters
at S.T.P.

With liquids and solids, the volume of the mole is different
for each substance.

205. The Relation between the Mole and the Molecule. —
It happens that the mole of pyrite (FeS2 -= 120 grams) is just
twice the mole of quartz (Si02 = 60 grams). The weights of
the molecules, if the oxygen atom equals 16, are represented
by the same numbers (120 and 60), so that the weight of each
molecule of the pyrite is twice as great as that of each mole-
cule of the quartz. 'Then the mole of pyrite must contain
the same number of molecules as the mole of quartz. We
take twice as much of the pyrite to make a mole, but each
molecule is twice as heavy, so the number of molecules in the
mole is the same.

It also happens that the mole of mercuric oxide (HgO =
216 grams) is 12 times that of water (H2O = 18 grams).
Again the moles of the two substances must contain the same
number of molecules. For we take twelve times as mutch
of the mercuric oxide, but each molecule of it weighs twelve
times as much as each water molecule.

From these examples it is easy to see that the moles of all
substances contain the same number of molecules.

Calculations made by very different methods agree that the number
of molecules in a mole cannot be far from 6 X 10^ (i. e. 6 followed by
23 ciphers) . In order to get a rough idea of the vastness of this number,
let us imagine that a mole (216 grams or about half a pound) of mercuric
oxide is heated in such a way that a million molecules are decomposed
into mercury and oxygen every second. It would be twenty thotisand
million years before the change was complete. This is about four
million times the total period that has elapsed from the dawn of his-
tory to the present time.

The same calculations make the probable diameter of simple mole-

168 AN INDUCTIVE CHEMISTRY

cules, like those of hydrogen and oxygen, about one ten-millionth of a
millimeter. This is about icfce the wave-length of violet light. The
circles in Fig. 59 represent the diameters of the molecules of some
familiar substances, magnified ten million times. The circles do not

OhJorafocm Alcohol Hydrognn

Staroh

FiQ. 59.

represent the shape in any way. Magnified on the same scale, a human
red blood-corpuscle would be a disc 70 meters in diameter.

2o6. Moles of the Elements. — The weight of a liter of
oxygen at S.T.P. is 1 . 429 grams. Then the weight of a mole
of oxygen, 22 . 4 liters, must be

1.429 X 22.4 = 32 grams.

Accordingly, the mole of oxygen contains two chemical
unit weights of 16 grams and the formula (not the symbol) of
oxygen is O2. Since we can read the mole formula directly
as a molecule formula, this means that the molecule of oxy-
gen gas is a group of two oxgyen atoms.

The weight of a liter of hydrogen at S.T.P. is .09 gram.
The weight of the mole is

.09 X 22.4 = 2.016 grams.

Since the chemical unit of hydrogen (atomic weight) is

THE ATOMIC THEORY

169

1 . 008, the formula is H2. The hydrogen molecule is a group

of two atoms.

This is always a difficult point. In order to attain perfect clearness
upon it, think of a mole of carbon dioxide, 44 grams, occupying, at
S.T.P., 22.4 liters. Now imagine the 12 grams of carbon removed. A
mole of oxygen, 32 grams, would remain and the volume would be un-
changed. Since equal volumes of gases contain equal numbers of mole-
cules, this shows that the number of molecules has remained the same
— each molecule of carbon dioxide has yielded a molecule of oxygen.
Since each molecule of carbon dioxide contains two atoms of oxygen,
each molecule of oxygen must contain two oxygen atoms. Repre-
senting the volumes by cubes 1% the side and josis the capacity of
those which would be required to contain the gases, we have: —

A mole of carbon dioxide.

A mole of oxygen.

As a matter of fact, we have seen that carbon dioxide does contain
its own volume of oxygen (p. 99). Exactly the same argument can
be used with sulphur dioxide.

Now think of a mole (28 grams) of carbon monoxide, CO, occupjring
22.4 liters at S.T.P. Remove the 12 grams of carbon. 16 grams, or
one-half a mole, of oxygen remain, which will fill 11.2 liters. From
Avogadro's hj^jothesis it follows that the number of molecules of oxy-
gen is haK as great as that of the carbon monoxide molecules. The
atoms of oxygen, as they were set free from the carbon monoxide, have
united in pairs and again we find that an oxygen molecule contains
two atoms.

207. Molecular Equations. — Substances are found to en-
ter into chemical changes in the quantities represented by the
chemical formulas, that is, in moles. Or, in the language of
the atomic theory, chemical changes take place between
molecules.

160

AN INDUCTIVE CHEMISTRY

It follows from this that chemical equations ought, in
strictness, to be written so that all the substances are present
as molecules. A single atom has no right to appear unless
the molecule of that substance really contains only one atom.
Some of the equations we have been using do not satisfy
this requirement. We can now revise them.

Inexact Form

CO + a >• CO2

SO2 + O — >• SO3
H2 + O — >• H2O

HgO — >• Hg + O

Revised Form

2C0 + O2 >- 2CO2

2SO2 + O2 >- 2SO3

2H2 + O2 >- 2H2O

2HgO >- 2Hg +O2

It will be noted that, in the last equation, the mercury is
allowed to remain as single atoms (2 Hg) and not represented
as a molecule of two atoms (Hg2). The reason is that it has
been proved that there is only one atom in the mercury mole-
cule: the molecule and the atom are identical. This is also
the case with all the other metals. It is true, also, of the
inactive gases of the argon group.

The moleculea of the active non-^metals are composed of a
group of atoms. The following table gives some information
on this subject. When read as moles, the formulas give the
number of grg^ms which are (or would be) contained in 22 . 4
liters at S.T.P. In terms of the theory, they express the
number of atoms in the molecule of the various substances:

Nam^

Symbol

At<ymic Weight

Formvla

I Oxygen

2 Nitrogen

3 Hydrogen

1.008

4 Chlorine .

35.5

CI,

5 Phosphorus

P«

6 Sulphur

f At low temperatures Ss
\ At a red heat Si

7 Mercury

200

8 Carbon

Unknown

THE ATOMIC THEORY 161

208. Discussion of the Table. — In the study of chemistry, we should
never be satisfied with a mere knowledge of the facts. The essential
thing is to get a firm grasp of the process by which the facts are obtained
— ^the evidence on which they are based. Let us discuss the table
briefly from this point of view.

The student will be ready to accept the formulas of the first four
elements without comment. They are gases, and he knows that, to
find the molecular weight, we have only to weigh a liter at S.T.P. and
multiply by 22 . 4. Thus, the weight of a liter of chlorine gas (Chap.
XVI) at S.T.P. is 3 . 17 grams. Then the weight of the mole (molec-
ular weight) is,

3.17 X 22.4 = 71.

The atomic weight of chlorine is 35 . 5 (see table on inside of back cover).
Hence the number of atoms in the molecule is

71 -5- 35.5 = 2,

and the formula is CU.

Sulphur cannot be obtained in the state of gas or vapor at S.T.P.
It can, however, be obtained as vapor at a higher temperature, and
the weight of a liter determined. From this weight by methods which
are discussed in Chap. XXX, the weight of 22.4 liters of sulphur vapor at
S.T.P. can be calculated. The same method can be employed with
phosphorus and with mercury, but not with carbon.

209. Molecular Weights of Dissolved Substances. — Until the close of
the 19th century the only way to determine the molecular weight was
to weigh the gas or vapor of the substance. A great step in advance wea
taken by RaouU when he made it possible to determine the molecular
weight of dissolved substances (Chap. XX). Thus stiZpAwr dissolves in
carbon disulphide and, from the behavior of the solution, the molecular
weight, of the dissolved sulphur can be ascertained. It is found, like
sulphur vapor, to have the formula Sg. These methods are valuable
in dealing with substances which cannot be converted into vapor.
Sugar, for instance, yields no sugar gas when heated, but chars and
passes into new substances. But by dissolving it in a suitable liquid,
its molecular weight can easily be obtained.

When a solid substance can neither be vaporized nor dissolved with-
out chemical change, its molecular weight remains imknown. The
substances to which we have given the formula ZnS, FeS, Fe804 and
Fe203 are of this kind. There is no way, at present, of determining the
weight of the molecules of these compounds. We therefore use the
simplest formula which will express the chemical composition. For-
tunately, this is suflScient for all practical purposes.

162 AN INDUCTIVE CHEMISTRY

210. Practical Advantages of Molecular Equations. — ^We
have seen that chemical equations give a complete account
of the proportions by weight according to which chemical
changes occur. Plainly this knowledge is essential to the
proper carrying out of any chemical process. Let us now see
what additional information is contained in molecular equa-
tions, that is, in those which we have revised so that free
atoms do not appear in them. For the combination of
hydrogen and oxygen, we have:

2H2 + O2 — >- 2H2O.

EJqual volumes of gases contain equal numbers of molecules.
Hence the equation means that:

2 volumes , 1 volume 2 volmnes of steam

of hydrogen of oxygen (above 100**).

Since two molecules of hydrogen and one molecule of oxygen
yield two of steam, the volume of the steam (above 100°) is
equal to that of the hydrogen at the same temperature and
pressure. The total volmne is reduced by the combination
in the ratio of 3 : 2.

Below 100® (p. 117), the steam condenses and the liquid water oc-
cupies a volume which is very small compared with that of the gases
which produced it. This volume is easily calculated. Reading the
equation in moles we have:

4 grams hydrogen + 32 grams oxygen >• 36 grams water.

44.8 Uters 22.4 Uters

Since the specific gravity of water is unity, the volume of the 36 grams
of liquid would be 36 c.c. This is only tAo of the volume of the gases
(67,200 c.c.) which combined to form it. The eudiometer (p. 117) for
lecture-experiments on this subject is usually graduated to i c.c.
Assuming that we exploded 30 c.c. of the mixed gases, the volume of the
liquid water would be:

30 X = — cc,

1800 60 '

THE ATOMIC THEORY 163

which could not be measured. This explains why it is disregarded in
actual work.

From Avogadro's hypothesis it is plain that in any equa-
tion dealing with gases, the coefficients giving the numbers of
molecules can be directly read as though they represented
volumes. The equation:

2C0 + O2 — ^ 2C0t
indicates, among many other things, that

2 volumes , 1 volume 2 volumes

carbon monoxide oxygen carbon dioxide.

Suppose that an open hearth furnace (p. 148) is heated with
producer gas containing 25% of carbon monoxide. What
volumes of gas and air should be admitted to it to give com-
plete combustion? For every cubic meter of oxygen we need
2 cu. m. of carbon monoxide. Since each cubic meter of
air contains 0.2 cu. m. (^ of its volmne) of oxygen, to get
one cubic meter of the latter we need u?y, or 6 cu. m. of air.
To get* the 2 cu. m. of carbon monoxide, we must take ir.lir
= 8 cu. m. of producer gas. So that the equation indicates
that the gas and air should be used in the ratio 8 : 5 by
volume. Since an excess of oxygen is necessary, more air
than the theoretical proportion would be admitted in
practice.

Questions about the volumes of gases Uberated during
chemical changes can be quickly answered from the molec-
ular equation, e. g.: What volmne of oxygen, measured at
S.T.P., will be produced when 9 grams of mercuric oxide are
heated?

2HgO — ^ 2Hg + O2
432 grams 22.4 liters

Evidently the answer is:

=^X 9 = 0.467 liter or 467 c.c.
432

164 AN INDUCTIVE CHEMISTRY

How much mercuric oxide must be heated to miake a liter of
oxygen at S.T.P.? The solution is:

432

22.4

= 19.3 grams.

On account of their greater simplicity, we shall continue,
in some cases, to use equations in which free atoms appear.

Related Topics

211. Review. — We have seen (pp. 154—6) that the atomic
theory gives a simple explanation of the four great laws of
chemical combination by weight. Let us state these laws again,
in the language of the theory.

1. The law of definite proportions. The molecules of the same
compound are all ahke. They contain the same number of
atoms of the same kind. The weights of these atoms are
constant.

2. The law of mvUiple proportions. Suppose that, into the
molecule of a compound AB we introduce more of one element
B, while the quantity of the other element A remains thS same.
Since the atoms are not divided we must introduce at least an
additional atom of B, and the new compound will be AB2.

3. The law of the indestructibility of matter. It is an experi-
mental fact that the weight of a sealed vessel is not altered by
any process (chemical or otherwise) which takes place in it.
Theoretical statement: Atoms cannot be created nor destroyed.
Chemical changes merely alter the way in which they are
grouped to form molecules. However, recent advances in
our knowledge of radium, and other radio-active substances,
have decidedly changed our views with respect to the complete
permanence of the atom (Chap. XXVII).

4. The atomic weights. The experimental fact: there is a
natural chemical unit for each element; a number of parts by
weight in which it enters into combination. By means of these
numbers, and small whole multiples of them, the composition of
all compounds can be expressed.

A moment's thought will show that this statement really in-
cludes the three laws just stated. For:

THE ATOMIC THEORY 165

(a) If iron and sulphur unite always according to fixed num-
bers (56 : 32), the composition of iron sulphide must always be
the same.

(b) Since sulphur always enters into compoimds as a quantity
of 32 parts, if we introduce more sulphur into iron sulphide we
must introduce 32 additional parts. Hence pyrite (FeSi) must
contain twice as much sulphur, for the same weight of iron, as
iron monosulphide (FeS).

(c) 56 parts of iron unite with 32 parts of sulphur to form a
molecular weight (56 + 32 = 88 parts) of iron sulphide. Plain-
ly, nothing is gained or lost in the combination. So that, in this
case, the law of the indestructibility of matter is simply the fact
that the molecular weight of a compound is the sum of the atomic
weights of its elements.

Theoretical statement: The atomic weight numbers ai:e
simply the relative weights of the atoms. The number 16 is
designed to the oxygen atom, and the other numbers are calcu-
lated upon that basis.

212. The Law of Combining Gas Volumes. — Chemical inter-
actions take place between molecules, and the number of inter-
acting molecules is always small. Since equal volumes of gases
contain equal numbers of molecules, if

1 molecule of a gas A interacts with 1 molecule of a gas B,

1 volume of A will interact with 1 volume of B.

If 2 molecules of A interact with 1 molecule of B

2 volumes of A will interact with 1 volume of B,

and so on. According to Avogadro's hypothesis, there must
always be a simple relation between the volumes of the two
gases. This is the theoretical statement of the law of combining
gas volumes.

213. Historical. — Democntus (5th century B.C.) declared
that matter was composed of particles which he called atoms,
and that between them was empty space. Twenty-three cen-
turies elapsed before John Dalton, of Manchester, in 1803, con-
ceived that these atoms must have definite relative weights,
which could be determined by the analysis of compounds.
Recent investigations so strongly confirm the statement that
matter has a granular structure, that it must be regarded at pres-

166 AN INDUCTIVE CHEMISTRY

ent as an established fact. We have just seen that the theory
explains perfectly the laws of chemical combination. One thing,
however, it leaves unexplained; the sudden change in all the
properties of substances, which, as we have often pointed out, is
the most striking feature of chemical changes. Why should the
chemical union of mercury and oxygen yield a red powder? of
copper and sulphur a black solid? of carbon and sulphur, both
of which are odorless solids, a strongly smelling liquid? Count-
less questions of this sort might be asked. Every chemical
process suggests one or more.

Definitioiis

Atoms. The smaller particles of which molecules consist.
Mole. The gram-molecular weight; the molecular weight, taken
in grf^iwr'

CHAPTER XIII

COMPOUNDS OF HYDROGEN WITH SULPHUR AND
NITROGEN— LIQUEFACTION OF GASES.—

REFRIGERATION

214. Interaction of Sulphur and Hydrogen. — ^When a glass
tube containing 0. 1 gram of sulphur and 100 c.c. of hydrogen
is sealed and gently heated (300**) for a week, the sulphur dis-
appears. When the tube is
opened, a gas escapes which
is clearly not hydrogen, for
it has a powerful, impleasant
odor and it immediately
blackens a clean piece of
copper. Hydrogen is odorless
and has no effect upon
copper.

This gas must be a com-
pound of hydrogen and sul-
phur. It is therefore called
hydrogen sulphide. Larger
quantities of it can be ob-
tained by the method de-
scribed in the laboratory studies (interaction of iron sulphide
and dilute hydrochloric acid). The Kipp apparatus (Fig.
60) is convenient. The interaction takes place according
to the equation

FeS + 2HC1 — ^ FeCla + H2S.
Iron Iron Hydrogen

Sulphide Chloride Sulphide

215. Formula of Hydrogen Sulphide. — Hydrogen sulphide contains
its own volume of hydrogen. This can be proved by the apparatus of
Fig. 61. The flask is filled with hydrogen sulphide. There is a little
tin in the bottom. The U-tube contains mercury covered with a layer
of oil in the limb next the flask.

167

FiQ. 60. — ^The Kipp apparatus.

168

AN INDUCTIVE CHEMISTRY

FiQ. 61. — ^Heating tin in hydrogen
sulphide.

By the cautious application of a flame to the bottom of the flask, the
tin is gently warmed. It combines with the sulphur, liberating the
hydrogen, which is found, after cooling, to occupy the same volume as
the hydrogen sulphide. This means that a mole of hydrogen sulphide

contains a mole (2 . 016 grams or two
chemical unit weights) of hydrogen.
In other words, the molecule of hydro-
gen sulphide contains two atoms
of hydrogen. For each molecule has
yielded a molecule of hydrogen, and
we have seen that the latter contains
two atoms.

A liter of hydrogen sulphide weighs,
at S.T.P., 1 . 522 grams. Hence the
weight of the mole is 1.522 X 22.4
=» 34.08 grams. Subtracting the
2.016 grams of hydrogen we have
left 32.06 grams of sulphur in the
mole. Since this is one atomic weight
of sulphur, the formula of hydrO'
gen sulphide is HiS.

2i6. Occurrence and Proper-
ties. — Hydrogen sulphide is contained in volcanic gases
and in the waters of sulphur springs. Eggs contain sulphur,
especially in the white portion, and, when they decompose,
hydrogen sulphide is Uberated. This is the cause of the
odor of rotten eggs. A trace of hydrogen sulphide escapes
when a boiled egg is opened, even though the egg is
perfectly fresh.

Hydrogen sulphide is a colorless gas which, by cold and
pressure, has been converted into a colorless liquid and into
an ice-like solid. A Uter of water at room temperature dis-
solves about 3 liters of it, alcohol twice as much.

Hydrogen sulphide bums with a blue flame, the hydro-
gen to water, the sulphur to sulphur dioxide. The latter
is easily recognized by its odor; the water by the dew which
deposits when the flame is allowed to bum in a cold bottle.
When the flame is cooled by placing a porcelain dish or a
glass plate in it, sulphur deposits upon the cold body.

COMPOUNDS OF HYDROGEN 169

At a red heat, hydrogen sulphide is decomposed. When
it is led through a heated glass tube, sulphur deposits, while
hydrogen passes on. It follows that, when hydrogen sul-
phide is burned, it must separate into its elements
before union with oxygen occurs. This explains the
deposit of sulphur when a cold object is introduced into
the flame.

217. Use of Hydrogen Sulphide. — ^When exposed to hydro-
gen sulphide, a piece of copper or silver at once becomes
covered with a black film of sulphide:

Cu + H2S — >• CuS + H2.

Many other metals behave in a similar way. Sulphides are
formed also, when hydrogen sulphide is made to bubble
through water in which compounds of certain metals are
dissolved. Thus, distilled water, when allowed to stand in
contact with lead, acts chemically upon the metal and dis-
solves traces of lead compounds. Some natural waters do
the same. On account of the intense poisonous action
of lead, it is often important to ascertain whether a water has
dissolved any lead compounds from the lead pipes which are
frequently used in plumbing. This can be done by passing
hydrogen sulphide through, the water by means of a glass
tube. If the water contains even as Uttle as a milligram of
lead per liter — one part in a million parts of water — its pres-
ence is revealed by a dark-brown precipitate of lead sulphide.
In water containing a dissolved cadmium compound, hydro-
gen sulphide produces a bright yellow precipitate of cad-
mium sulphide, CdS. Many of the other metal sulphides
are insoluble in water and are formed in a similar way. For
this reason hydrogen sulphide is constantly used in the
laboratory in the detection of the metals and their separation
from each other.

218. Action upon the Body. — Hydrogen sulphide is
poisonous. In working with it, care should be taken to in-
hale as little as possible. The coloring matter of the red

170 AN INDUCTIVE CHEMISTRY

corpuscles is an iron compound called hemoglobin. Hydro-
gen sulphide removes the oxygen from the corpuscle:

HsS + ^ HsO + S

and, at the same time, converts the iron into iron sulphide.

The blood, therefore, becomes incapable of supplying the

body with oxygen,

219. Hydrogen Disulphide. — Hydrogen disulphide, HiSj

is a yellow oil, which separates into hydrogen sulphide and

sulphur when preserved. It is of no special significance, but
the corresponding
oxygen compound,
kydrogen peroxide,
HiOj, has important
applications I'Chap.
XXIV).

220. Ammonia:
Preparation. — The
familiar ammonia-
waler, so much used
in the household, is
a solution of am-
monia gas in water.
The gradual escape
of the gas is the

Fia. 02. — PiepsratioQ ol unmoBis rm from e j.i. i.

Bmmonis water. CEUSC Of the sharp

odor of the hquid.
Like most other dissolved gases, it escapes almost completely
when the solution is heated and one method of preparing
ammonia-gas is based upon this fact. Some steam is mixed
with the gas prepared in this way, but this can be removed
by passing it through a tube filled with small lumps of lime.
This absorbs the water, forming slaked lime, while the dried
ammonia gas passes on.

A better method is to allow ammonia-water to fall from
a dropping funnel upon caustic potash (Chap. XX), Being

COMPOUNDS OF HYDROGEN 171

very soluble in water, the caustic potash absorbs the water,
and the ammonia gas is set free in dry condition (Fig. 62).
On account of the solubility of the gas in water, water can-
not be used for collecting it.

Down to 1770, water was the only liquid employed for collecting
gases, and those which were freely soluble in it were absorbed and
escaped detection. About that time it occurred to Priestley to try
mercury and he at once discovered a number of gases, among which were
ammonia and sulphur dioxide. Hydrogen sulphide had been discov*
ered by Scheele a few years before.

221. Physical Properties. — ^At room temperature, a pres-
sure of about seven atmospheres converts ammonia into a
colorless liquid. The same result is obtained, imder ordinary
pressure, by cooling to -34**. This liquid is largely used in
ice-machines. Ammonia is one of the very soluble gases.
Water dissolves at 0** more than 1000 times its volimie, and
at ordinary temperatures, about 700. The strongest am-
monia-water of commerce has a specific gravity of about . 9

and contains about 35% of ammonia by weight.

222. Composition. — ^When a mixture of nitrogen and hydrogen is
treated with electric sparks the odor of ammonia appears. On the
other hand, when ammonia itself is '^sparked,'' its volvune is doubled and
the gas is found to consist of nitrogen and hydrogen.

Two conclusions follow:

1. Ammonia is a compound of nitrogen and hydrogen.

2. The reaction,

nitrogen + hydrogen ^ ^ ammonia

under the influence of electric sparks, proceeds forward or backward
according to the concentration. So long as the percentage of ammonia
in the gas is leas than three y nitrogen and hydrogen unite; but in pure
anmionia or in any gas containing more than three per cent of it,
ammonia is decomposed into nitrogen and hydrogen.

In order, then, to make nitrogen and hydrogen unite completely,
we must "spark" the mixture in such a way that the ammonia is re-
moved as fast as it is formed. This is easily done by confining the gases
in a eudiometer over dilute sulphuric acid, which at once absorbs the
ammonia, forming with it a compound we shall study later (Chap. XXII).
When a mixture of one volume of nitrogen with three volumes of hydro-
gen is treated in this way, all gas disappears and the liquid slowly rises

172 AN INDUCTIVE CHEMISTRY

to the top of the tube. Remembering that the nitrogen molecule is
Ns and that of hydrogen H2, it follows that the molecule of ammonia
contains three atoms of hydrogen for one of nitrogen — the simplest
formula is NH3.

That this is the correct formula is shown by the determination of the
weight of 1 liter of ammonia at S.T.P., which is 0.76 gram. The
molecular weight must be:

0.76 X 22.4 = 17

and this corresponds to the formula NH|.

223. Chemical Properties. — When a tube, from which am-
monia is escaping, is held near the Bimsen flame, the ammo-
nia bums in the Bunsen flame, with a yellowish color, but does
not continue to bum when the flame is withdrawn. The ex-
planation is that, like other hydrogen compounds, the am-
monia must be decomposed by heat before the hydrogen can
bum:

2 NHa — ^ N2 + 3H2.

The hydrogen then bums to water, while the nitrogen is
liberated. In oxygen, ammonia burns with a continuous
flame, which has a high enough temperature to separate the
gas into nitrogen and hydrogen, and thus to provide the fuel
necessary to its own existence.

Ammonia is decomposed by a red heat, according to the
equation just given. When it is led through a hot glass tube,
the mixture of nitrogen and hydrogen which collects is com-
bustible and occupies twice the volume of the ammonia.

224. Occurrence. — The atmosphere contains traces of
ammonia. Natural waters sometimes contain it. There is
never enough to be harmful — less than one part per million by
weight — but its presence is often an indication that the water
has been recently contaminated by sewage, and may contain
the typhoid germ.

Ammonia is produced during the decay of animal and plant
matter. For this reason its odor is usually noticeable around
stables, cesspools and manure-piles. The same fact explains
the occurrence of ammonia in the soil, which always contains

LIQUEFACTION OF GASES 173

it. It is an important plant-food, but it cannot be absorbed
by the roots imtil after it has been oxidized to nitric add
(Chap. XXIII).

225. Source and Uses. — Bituminous coal contains about
2% of nitrogen with much larger quantities of hydrogen.
It is not surprising, therefore, that, when coal is distilled for
the manufacture of illuminating gas or of coke, ammonia
is always produced. This is the source of all of the ammonia
of commerce.

The use of liquid anunonia for refrigeration has been men-
tioned. Ammonia water is widely used for scouring and
cleansing. The use of ammonia gas in the manufacture of
washing soda is important (Chap. XXIV). Great quanti-
ties of compounds containing ammonia (Chap. XXII) are
used as fertilizers.

226. Other Compounds of Nitrogen and Hydrogen. — Hydrazine ^
N2H4, is a colorless liquid, which smells like ammonia, which it strongly
resembles in properties.

Hydrazoic addy NsH, is a colorless liquid with an intolerable smell.
It is highly explosive. It differs widely from ammonia in properties,
being more like hydrochloric acid than anmionia in chemical behavior.

Related Topics

227. The Liquefaction of Gases, the Nature of Liquefaction. —

The chief distinction between liquids and gases is that the mole-
cules, at ordinary pressures, are more crowded in the former.
While 3 X 10^^ molecules fill a liter in the state of gas, the same
number of molecules in the liquids is crowded into a volume
which, on the average, would hardly be greater than a cubic
centimeter. According to the kinetic theory, it is the rapid
straight-line motion of the gas molecules which keeps them dis-
tributed evenly and prevents them from settling to form a
layer of liquid on the bottom of the vessel. This motion is heat.
This suggests three methods of liquefying gases:

(a) To rob the molecules of their heat motion by cooling.

(b) To crowd the molecules closer by pressure.

174 AN INDUCTIVE CHEMISTRY

When these conclusions are tested by experiment, it is
found that:

(a) All gases could indeed be liquefied by cooling, were it not
that the temperature required is often so low that it is difficult
or impossible to reach it. Thus, sulphur dioxide, under one

atmosphere pressure, liquefies at
-8®, which can easily be obtained
by merely mixing ice and salt.
But hydrogen, under air-pressure,
requires a temperature of -253®,
while helium only assumes the
liquid state at -268®. 5, which is

Fig. 63.— a Faraday tube. witMn 4® . 5 of the absolute ZCrO

of Physics.

(b) The effect of pressure alone upon gases has been discussed.
§ 90 should be re-read.

(c) The only possible conclusion is that, in most cases, it is
necessary to apply pressure and cold simultaneously. This
method, after much brilliant work, has led to the liquefaction of
all gases. Helium was the last to yield.

228. The Faraday Tube. — Michael Faraday, in 1823, was
the first to attack the problem in a systematic way. He em-
ployed a bent sealed tube of thick glass, called, after him, the
"Faraday tube" (Fig. 63). In one limb was placed the mixture
generating the gas which he desired to liquefy. The other limb
was placed in a freezing mixture. The pressure was furnished
by the continued production of the gas in a closed space. Far-
aday had no difficulty in liquefying sulphur dioxide, ammonia,
carbon dioxide, hydrogen sulphide and many other gases by
this simple method. Others, like hydrogen, nitrogen, and oxy-
gen, showed no evidence of liquefaction.

229. Liquefaction of Oxygen. — The method used by Pictet
(Dec. 22, 1877) in liquefying oxygen was the same in principle
as that of Faraday. The gas was generated in a strong wrought
iron retort and forced, under its own pressure, into a metal
tube closed by a stopcock. By means of solid carbon dioxide
(the evaporation of which was made more rapid by an air-pump)
this tube was cooled to -140**. Liquid oxygen escaped when the
stopcock was opened.

LIQUEFACTION OF GASES

176

Recent experimenters have largely worked along the same
line as Pictet, but they have used powerful pumps to compress
the gases and have employed more efficient methods of cooling.

330. Self-intensive Cooling. — When a compressed gas is
allowed to expand freely, it becomes a little cooler. There is a
slight attraction between the molecules of gases, and energy is
used up in separating them. The effect is slight — less than 1**

Fia. 64. — Preparation of liquid air.

— yet by a simple device due to Linde^ the cooling can be
accumulated until the gas becomes a liquid. A diagram of
Lindens apparatus is shown in Fig. 64. Air is compressed to 200
atmospheres and the heat produced is removed in a water-
jacketed cooler. It then passes through P2 into the liquefying
apparatus which consists simply of a double copper tube. The
compressed air passes down through the inner tube into the

176 AN INDUCTIVE CHEMISTRY

vessel F, where it expands and is slightly cooled (say 1®). Tak-
ing the temperature of the room as 20®, that of the expanded gas
is 19®. From F, it follows the upward arrows through Pi to the
^ace between the outer and inner tubes. Thus the freshly
compressed air in Pi on its way to V is cooled by the colder ex-
panded air. This second quantity of gas will have a tem-
perature of 19® before it expands and will drop to 18® afterward.
Thus the temperature in the liquefier falls until, after an hour
or so, liquid air can be removed at G, while fresh air is introduced
at C when necessary. In the actual apparatus, the double tube
is not straight, but is wound into a spiral. This makes it pos-
sible to give it a length of 100 meters, without
occupying too much space.

231. Liquid Air. — Liquid air is blue. When
poured upon the floor it instantly evaporates. Its
temperature is -192® and it produces a cloud of
condensed water drops in the air, just as ice does.
It can be kept for hours in a double-walled vacuum
vessel (Fig. 65). Like water, it must absorb heat
in order to evaporate, and heat reaches it slowly
in such a vessel, because a vacuum is the best
possible non-conductor of heat. This is the
principle of the vacuum bottles^ which have grown
Fia.65.— Avao- SO popular of late. They resemble Fig. 65, except
uum-jacketed ^^^^ ^j^^y g^j.g provided with a stopper and a

metal case.

232. Preparation of Oxygen on a large Scale. — Some freshly
liquefied air is poured into a vacuum vessel. From time to
time a splint bearing a spark is introduced into the upper part
of the vessel above the surface of the liquid. At first the spark
is extinguished. The nitrogen is escaping. After the vessel has
stood for a time, the spark when introduced is relighted, showing
that the gas now escaping contains much more oxygen than
ordinary air. The explanation is that the boiling-point of nitro-
gen (-194®) is lower than that of oxygen (-182®). Hence the
nitrogen, being the more vdlatile liquid, evaporates most rapidly.
This is additional evidence that air is a mixture.

From the boiling-point of the two gases, it will be seen that if
Lindens apparatus (Fig. 64) is run in such a way that only a

LIQUEFACTION OF GASES 177

fraction of the air is permanently condenaed, that fraction will
be cliiefly oxygen. Oxygen is now made commercially cliiefly
by this method, which is cheap because, with the exception of
the coal needed to run the engine for the pumps, the atmosphere
ia the only raw material required. Liquid air, made by Linde'a
method, is allowed to trickle over glass balls packed in a tall
column. The nitrogen evaporates and paseesoff through a tube
at the top, while liquid oxygen collects at the bottom.

There is a large field for oxygen in illumination and in me-
taUurgy, but the high price of the gas has hampered its applica-
tions. It is likely that the Linde method will reduce the price

IFio. 66. — The liquefnetioa ot hydrocen

to a point at which it will become possible to employ oxygen for
many practical purposes. The product contains some nitrogen
(about 5 %), but that does not interfere seriously with its use.

233/ Liquefaction of Hydrogen : Some Results. — Since Linde's
invention, aelf-intensive cooling and external cooling have often
been combined in low-temperature work. The apparatus used
by Dewar in the liquefaction of hydrogen (1898) is an illustration
(Fig. 66). C is a cylinder containing pure hydrogen under a
pressure of 200 atmospheres. Vi Fj and V3 are vacuum-
jacketed vessels (Fig. 65). Vi contained solid carbon dioxide,
Vt liquid air boiling rapidly in a partial vacuum. Thus, before
self-intensive cooling was begun, the hydrogen was cooled to

178 AN INDUCTIVE CHEMISTRY

-205°. Vf waa empty. It was sunk in a larger vacuum vessel
contaioing liquid air. The principle is the same as that of
Fig. 64. Liquid hydrogen coUected in Vj. Its properties
have been discussed (p. 116).

The lowest temperature thus far reached is -271°. 5. This is
within 1°.5 of the total absence of heat. Onnes obtained this
temperature by boiling liquid helium in a partial vacuum.

Most bacteria are rapidly killed by temperatures in the neigh-
borhood of 100°, but they are very resistant to cold. Long ex-
posure to the temperature of liquid air has no destructive action
upon them.

We have noticed the very important fact that all chemical
changes take place more rapidly at high temperatures than at

Fia. fl7. — AitiGcia] cooling azid ioe-mokiiig appuKtua.

low. At temperatures in the neighborhood of -200° the speed of
almost all chemical processes becomes so small that they may be
considered as not occurring ai all. Substances which interact
violently at room temperature remain in contact, without any
apparent change.

334. The Ammonia Ice Machine. — All liquids absorb much
heat when they evaporate. Refrigeration by machines is based
apon tliis fact. Liquid ammonia has largely displaced other
liquids because it is cheap and because, when it becomes am-
monia gas, it absorbs large quantities of heat, 300 calories for
every gram which evaptorates.

The diagram (Fig. 67) will make clear the principle of the ice
machine. The ammonia gas is forced, by a pump operated by a

REFRIGERATION 179

steam engine, into a coil of iron pipe, C, where it condenses, liberat-
ing 300 cal. of heat for every gram of liquid formed. This heat
is removed by water circulating outside the coil. The liquid
ammonia passes through a regulating valve into a second coil, E,
which is immersed in a tank of brine. Here, aided by the suc-
tion of the same pump, it evaporates, absorbing 300 calories of
heat per gram. Hence the brine becomes cold. If tin cans con-
taining water are hung in it, the water will be frozen. In cold-
storage warehouses, the chilled brine is circulated in iron pipes
through the rooms to be cooled. Dwellings might be supplied
with chilled brine from a central station, where the ice-machine
for the entire neighborhood was placed. This brine, passing
through a coil in the box where foods were kept, would make a
clean and efficient substitute for the ordinary refrigerator. The
entire house could be cooled, during hot weather, in the same
way, but the expense has thus far prevented the application of
the method.

CHAPTER XIV
COMPOUNDS OF CARBON AND HYDROGEN

235. Marsh-Gas. — When the rotting vegetable matter on
the bottom of a marshy pool is stirred, bubbles of 7narsk-gaa
escape. Fig. 68 shows an easy method of collecting the gas.
It is colorless and combustible, burning, when a lighted match
is applied to it, with a pale blue flame, not unUke that of
hydrogen. However, if we bum
a test-tube of the gas and then at
once shake up some lime-water in
the tube, the liquid becomes milky.
Carbon dioxide has been produced
by the combustion. This proves
that marsh-gas is a carbon com-
pound.

A current of marsh^as which

as been carefully dried is passed

through a glass tube and lighted

Fia. 68.— coiieotjonofmnreh-gM. at the orifice. When a dry cold

bottle is held over the flame, a dew

composed of fine drops of water deposits. Marsh-gas, then,

is a compound of carbon and hydrogen. Careful investigation

shows that when pure it contains only these two elements.

Quantitative work shows that marsh-gas contains 12 parts

of carbon combined with 4 . 032 parts of hydrogen by weight.

This points to the formula CH4. The weight of a liter of

pure marah-gas is 0,716 gram. Multiplying this by 22.4 we

get 16 . 03 as the molecular weight. This leaves no doubt

that CK, is the correct formula. It is often written more

fully thus:

H-C-H

COMPOUNDS OF CARBON AND HYDROGEN 181

This does not indicate the shape of the molecule of marsh-
gas. It means simply that the carbon atom is in the center
and that aroimd it are grouped four hydrogen atoms, each of
which is united to the central carbon atom in the same way.

236. Methane. — The chemical name of marsh-gas is
methane. It has been converted into a colorless Uquid
which has a specific gravity of only 0.41. Liquid hydrogen
(spec. grav. 0.07) is the lightest of liquids and liquid helium
(spec. grav. 0.15) is next. Liquid methane comes third.
Natural gas, by which whole cities in Pennsylvania, Ohio
and West Virginia are heated, is chiefly methane (90%).

Like all combustible gases, methane forms an explosive
mixture with air. This mixture is the fire damp (from the
German word Dampf, vapor) of the coal mines. Accidents
caused by fire damp are especially frequent in mines where
bituminous coal is obtained.

337. Coal Gas. — Methane makes up about one-third by volume of
coal gas which is much used for lighting in Europe and in smaller
American cities. Coal gas is made by distilling soft coal in cylin-
drical fireclay retorts (Fig. 69). Since the coal does not distill as coalj
but is destroyed or broken up, by the white heat applied, into simpler
substances, the process is called destructive distillation. The residue
left in the retorts is coke.

The result is a complex mixture. Recalling that soft coal contains
much carbon and hydrogen, along with oxygen, sulphur and nitrogen,
we might expect, among the substances we have studied, the following
to be formed:

Hydrogen
Methane

Carbon monoxide
Carbon dioxide
Carbon disulphide
Hydrogen sulphide
Ammonia

All of these substances and many others are, in fact, produced. The
last three in the list above must be carefully removed from the gas
before use, for they would cause it to produce an unpleasant odor when
burned. Many Uquid and solid compounds of carbon and hydrogen
18

182 AN INDUCTIVE CHEMISTKY

are formed, and these must be removed, since they would cbg up Iho
pipes. The purified gas variea in composition, according to the coal
and the temperature. An
average is the following:

I 1. Hydrogen

I 45% by volume

2. Methane

33% by volume

3. Otiier compounds of

carboD and hydro-
gen 5% by volume

4. Carbon monoxide

14% by volume

5. Nitrogen

3% by volume

i We shall examine into the
_ nature of the compounds in
E (3) shortly. One metric ton
^ of good coal yields about
I 300 cu. m. of gas (1 cu. m.
I = 35.3 cu. ft.),
s 338. Hanufactore of Coal
3 Gas. — The process of the
1 manufacture of coal gas is
. best underatood from the
i§ diagram (Fig. 69). From
the retort a tube takes the
gasee up to the hydraidie
main. Tins is a horizontal
pipe running at ri^t-angles
to the retorts. Here much
liquid and solid matts' col-
lects. The rest is removed
by the condenser, a long
series of iron pipes with a
box at the bottom for the
collection of oily and tairy
products. These, with the
material from the hydraulic
main, flow into the tar uwfi and make up the mixture called coof tor.
An exhaust now transfers the gas to the aerubber, a tall iron tower in
which water trickles down over coke or woodoi slats to remove the

COMPOUNDS OF CARBON AND HYDROGEN 183

ammonia and hydrogen sulphide. Then follows the purifier, an iron
box with perforated shelves, filled with ferric oxide. The gas then
goes through a meter into the holder, from which it is distributed to the
consiuners.

239. Hydrocarbons of Coal Gas. — ^A compound of carbon
and hydrogen is called a hydrocarbon. Since hydrogen, car-
bon monoxide and methane all burn with a pale blue flame,
the light-giving quality of coal gas must be due to the five
per cent, of hydrocarbons mentioned in (3) §237. This
five per cent, is made up roughly as follows:

Acetylene, C2H2 1.5% by volume
Ethylene, C2H4 2.5% by volume
Benzene, CeHe 1 % by volume

Methane, CH4, contains 75% by weight of carbon: these three
hydrocarbons contain more, as the formulas show. Ethy-
lene contains 86% and acetylene
and benzene (which clearly have
the same percentage composition) ^
contain over 92% of carbon by ft^r^

weight. All three are decomposed

by the heat of the flame, before

they combine with oxygen, and the

fine particles of solid carbon which

separate glow brightly; hence the ^^- ''e^i^?'^ "'

fight.

240. Acetylene. — ^When hydrogen is slowly passed through
a globe in which the electric arc is burning between carbon
poles, acetylene is formed (Fig. 70). The reaction is strongly
endothermic:

2 C + H2 — >- C2H2 — 58,000 cal.

Acetylene can be easily made by the interaction of water and
calcium carbide. This is a hard iron-black solid which may
be familiar to the student from its use in automobile and
bicycle-lamps. It is a chemical compound of carbon with a
metal, caicium, which we shall study later. One kilogram of

184 AN INDUCTIVE CHEMISTRY

the commercial carbide, brought into contact with water,
yields about 300 liters of acetylene. Automatic apparatus is
constructed by which the carbide is gradually fed into a
large volume of water. The gas is purified and stored in
small gas holders.

241. Properties. — ^Acetylene is a colorless gas with an im-
pleasant smell. When mixed with air it explodes violently
on contact with flame. It is readily liquefied by pressure
alone, but the liquid is a dangerous explosive. Endothermic
compounds, which, Uke acetylene, are formed from their
elements with absorption of energy, are, in most cases, ex-
plosive. The explosion of liquid acetylene (in absence of air)
is simply sudden separation into hydrogen and carbon. The
energy which was absorbed in the combination is violently
Uberated.

242. Use. — On account of its richness in carbon, acetylene
produces a sooty flame when an ordinary burner is used with

it. A good burner for it is shown in
^ Fig. 71. Air is drawn in through the
/ side-holes on the Bunsen principle.
^'^ The two flames strike each other and
broaden out into a single flame at
right-angles to the plane of the
burner. This flame is intensely bright
_ and its light resembles simlight closely :

acetylene. hcncc the acctylcne light is excellent

for judging colors. A liter of acetylene
gives about as much light as twenty liters of coal gas. It
is much used for illumination in the country, in localities
remote from a gas-works. Copper gas-holders or pipes must
not be used in handling acetylene, for it forms a highly ex-
plosive compound in contact with this metal.

243. The Acetylene Blowpipe. — The combustion of any
hydrocarbon results in the production of carbon dioxide and
water. Acetylene, burning in oxygen, produces the hottest
flame known. Its temperature is close to that of the electric

COMPOUNDS OF CARBON AND HYDROGEN 185

arc (nearly 4000"*). The reason becomes clear when we con-
sider that the gas is an endothermic compound. The 58,000
calories, which are absorbed when acetylene is formed from
its elements, are again liberated when it is decomposed in the
flame. When acetylene bums, we obtain 100,000 cal. for each
of the two atomic weights of carbon, 70,000 cal. for the two
atomic weights of hydrogen, and, in addition, the 58,000 cal.
from the decomposition of the gas before it bums. So the
thermochemical equation is:

C2H2 + 50 — >- 2CO2 + H2O + 328,000 cal.

The burner employed is shown in Fig. 72. It is often
called the oxy-hydrogen fetoiyptpe, because it was first used with
hydrogen and oxygen. It consists of an inner tube, convey-
ing the oxygen, surrounded

by a larger one which — --?^

carries the acetylene. The ^ C"

Fig. 72. — The oxy-hydrogen blowpipe.

burner does not melt be-
cause the base of the flame
is comparatively cool.
The oxy-acetylene flame is much used in working metals.
A six-inch shaft of solid steel has been cut in two with it in
less than forty seconds, while, in another test, a circle twenty
inches in diameter was cut out of one-inch steel plate in
forty-five seconds.

244. Benzene. — ^When acetylene is passed through a hot
tube some of it is converted into benzene.

3 C2H2 — ^ CeHe .

Benzene (which must not be confused with the benzine from
petroleum) is a colorless liquid which takes fire readily,
burning with a smoky flame. It is formed by the distillation
of soft coal, and some of it passes as vapor into the coal gas,
but most of it collects, as a liquid, in the hydraulic main and
the condenser, and is found in the coal tar.

186 AN INDUCTIVE CHEMISTRY

245. Naphthalenei Anthracene. — Two other hydrocar-
bons of coal tar must be mentioned on accomit of their com-
mercial importance.

Naphthalene, Cio Hg, is known commercially as "moth
balls/' "tar balls" and "tar camphor." Coal tar contains
nearly ten per cent, of it. It is contained in coal gas and
sometimes causes trouble in winter by condensing in the
pipes and clogging them. It crystallizes in white shining
plates which have a tarry smell.

Anthracene, C14H10, forms colorless glistening leaflets. It
is important because it is used for the manufacture of the
important dye-stuffs which were formerly obtained from the
madder plant. Large quantities of benzene and naphthalene
are used for the manufacture of drugs, perfumes, photo-
graphic developers and dye-stuffs. These substances, thou-
sands of which have been prepared, are not contained in coal
tar. They are made, by complex processes, from the hydro-
carbons which are obtained from the tar by distillation.

Coal tar was formerly an annoying waste-product of the
gas-works. At present they are unable to supply enough
to meet the increasrug demands of chemical industry. For-
tunately, the rational manufacture of coke (p. 43) is a great
and growing source of coal tar.

246. Petroletun. — Petroleimi is an oily liquid found in
the rocks in certain localities, especially in Pennsylvania,
Ohio, Texas and California. It also occurs in Russia near
Baku on the shore of the Caspian Sea, where vast quantities
have been obtained from an area of only six square kilo-
meters.

When a well is first drilled, thousands of barrels of petro-
leum often spout from it per day. Later the pressure sub-
sides and the petroleum is pumped to the surface. It is dis-
tributed to the refineries by iron pipe-lines, which, in the
United States, have a total length of many thousand miles.
The world's production of petroleum is about 35 million tons
each year, of which the United States furnishes two-thirds.

COMPOUNDS OF CARBON AND HYDROGEN 187

247* Fonnation and Nature of Petroleum. — Petroleum was
probably formed from great accumulations of animal and
vegetable remains by a slow change in which a moderately
high temperature and great pressiu-e played an important
part. All petroleums are mixtiu-es of hydrocarbons. Penn-
sylvania petroleum is composed of hydrocarbons which
resemble methane closely in chemical properties, and are
therefore said to belong to the same series. The following
table gives a partial list of these hydrocarbons, with their
boiling-points and an indication of their uses:

Name

Formula

Boiling-
point

Commercial Name

Use

Methane

CH4

—160°

Natural gas

Fuel

Ethane

CjH»

— 93°

Profane

CsHa

— 46°

Butane

C4H10

1°

Pentane

CjHif

36° \
69°/

Mixture of the two is

Scouring and clean»-

Hezane

CeHw

called petroleum ether

ing agent for cloth,

etc., enriching water

gas

Heptane

O7H16

98°

Mixture of hexane
and heptane is called
napht?ui or gaaoline

Scouring and as fuel

Octane

CgHig

126°

Mixture of octane and

Like gasoline, fuel

Nonane

C9H10

160°

nonane is called ben-
zine

for automobiles, mo-
tor boats, etc.

Decane

CioH«

173° '

Mixture of these seven

•

hydrocarbons in vary-

Illuminating oil

Hezadecane

CwHm

287°^

ing proportions is kero-
sene

Bicosane

CjoHii

Solid (melts
at 37°)

Mixed with higher
members is called
paraffine

Candles, siiing, etc.

Hezacontane

CeoHiM

SoUd (melts
at 100®)

An inspection of this table reveals three important facts:

1. The number of hydrogen atoms in any member can be obtained by
multiplying the number of carbon atoms by two and adding two to the
product. Hence the formulas need not be memorized.

2. The formula of any hydrocarbon can be obtained by adding one
carbon atom and two hydrogen atoms (CH2) to that of the hydrocarbon
next below it in the series.

188

AN INDUCTIVE CHEMISTRY

3. The melting- and boiling-points gradually rise as we ascend in the
series, so that the first members are gases, the middle members Uquids;
and the higher members soUds. From pentane on the names are formed
by adding ane to one or two syllables of the Greek numerals.

348. Refining. — Some petroleums, especially those from Ohio, Texas
and California, contain, with the hydrocarbons, compounds of sulphur
and of nitrogen which make the refining difficult. Much oil of this
sort is burned in the crude state, as fuel for steamships and locomotives.
However, most petroleum is refined for use.

Refining is essentially a process of distillation in which the crude oil
is separated into a number of fractions which differ from each other in
boiling point and composition. No attempt is made to separate the
hydrocarbons themselves in pure condition. This can be done, but it
is too tedious and expensive for practical purposes. The fractions into
which the crude oil is separated are still mixtures, but of a few hydro-
carbons only.

The petroleiun is distilled from a horizontal iron cylinder into a coil
of pipe cooled by water. A thermometer, immersed in the vapor, con-
trols the process. The chief fractions, with the temperatures between
which they are collected, are indicated in the following table.

When the temperature rises to 300° the oil still remaining in the
cylinder is distilled by the use of a higher temperature and is placed in a
vessel where it is chilled by pipes containing brine from an ice-machine.

Commercial
Name

Composition

Temperatures

Petroleum ether

Gasoline

Naphtha

Benzine

Kerosene

C6H12 + CeHi4
CeHn H- C7H16
C7H16 H- CgHis
CsHis H- C9H20

C10H22 to C16H34

40° to 70°

70° to 90°

90° to 120°

120° to 150°

150° to 300°

Paraffine separates in crystalline plates. The portion which remains
liquid, in spite of the chilling, is used as lubricating oily for which purpose
it has largely displaced oils of animal and vegetable origin. Or, if in-
stead of distilling and freezing out the paraffine, the liquid remaining in
the cylinder is simply robbed of its dark color by filtering it hot through
bone-charcoal, it forms a pasty mass which is used as a lubricant and
ointment under the names vaseline, cosmoline or petroleum jelly.
The kerosene is further purified by shaking it with sulphuric acid and

COMPOUNDS OF CARBON AND HYDROGEN 189

then with caustic soda solution (lye). Itisfrom this fraction that the
necessity of the refining can be most easily understoC>d. If crude petro-
leum was put directly into a lamp, the lower hydrocarbons would mix
with the air above the oil and cause constant danger of explosion, while
the highest ones would clog the wick and give a smoky flame.

Gasoline, naphtha and benzine were formerly products for which it
was difficult to find a ready sale. At present the automobile and the
motor-boat have caused such a demand for them that they bring a
higher price than the kerosene. Since these three substances are often
used for cleansing in the household^ it should he noted thai the greatest care
must he taken to make sure thai no flame or fire is in the house when such
work is done. Shocking accidents often occur from slight carelessness in this
respect,

249. Ethylene Series. — Ethylene^ C2H4, is a colorless gas
which burns with a bright flame. It is the first member of
a series of hydrocarbons:

Ethylene C2H4

Propylene, CaHi
Butylene, C4H8, etc.

In this series, the number of hydrogen atoms is obtained by
multiplying the number of carbon atoms by two. The three
just named are gases, the middle members Uquids, and the
higher members solids like paraflSne. They can readily be
prepared from the corresponding members of the methane
series.

250. Acetylene Series. — Acetylene j C2H2, heads a third series
in which the number of hydrogen atoms is obtained by multi-
pljdng the number of carbon atoms by two and subtracting
two:

Acetylene, C2H2

Allylene, C8H4

Crotonylene C4He

There are also many hydrocarbons related to benzene, CeHe.
The total number of hydrocarbons known is upwards of two
hundred, of which some are found in nature (methane series)
but many are purely laboratory products. The number
which could be prepared is almost unlimited.

190 AN INDUCTIVE CHEMISTRY

251. Asphalt. — Asphalt, or "mineral pitch," is a hard, black,
combustible solicf with an odor recalling that of kerosene.
On the island of Trinidad there is a lake of it 13^ miles in
diameter, warm and soft in the center, but hard and cold near
the edge. Asphalt is chiefly a mixture of hydrocarbons, but
it also contains oxygen and sulphiu'. It is used in paving.

Definitions

Hydrocarbon. A compoimd of carbon and hydrogen.

Series. A group of related compoimds, similar in composition
and properties. The molecular weights gradually increase from
one compound to the next.

CHAPTER XV

SOME COMPOUNDS CONTAINING CARBON,
HYDROGEN AND OXYGEN

252. Starch Formation. — ^We have seen (p. 103) that,
under the influence of light, the leaves of plants decompose
the carbon dioxide of the air and give oflf oxygen. Unlike
the oxygen, the carbon does not separate in the free state.
It combines with water, which is abundant in plants, and
forms starch, CeHioOs, which may be regarded as resulting
from the combination of six atoms of carbon with five mole-
cules of water.

The solution of iodine which is used for the external treat-
ment of sprains and other injuries affords a delicate test for
starch. The result of bringing the two together is an intense
blue color. By the aid of this test, the fact that starch is
produced in the green portions of plants, when acted upon by
light, can be shown. A nasturtium plant, for instance, is
kept in the dark for a time, and a portion of a leaf is pro-
tected by fastening tin foil on both sides of it. The plant is
then exposed to light for some hours. The leaf is picked and
soaked, after removing the tin foil, in alcohol, which dissolves
the green coloring matter, turning the leaf white. It is then
transferred to a dilute solution of iodine, where in a short
time it turns bright blue wherever the light had access.
The portion which was protected by the tin foil remains
white, showing that no starch was formed there.

253. Properties. — Starch is a white powder, composed of
little grains called "starch granules,'' the size and shape of
which differ in different plants. It is possible, therefore, to
determine with the microscope the plant from which a given
sample of starch has been derived. It is an important ele-
ment in food, being largely contained in grains like rice, oats,
rye and wheat. Ordinary flour is about three-fourths starch.

191

192 AN INDUCTIVE CHEMISTRY

Potatoes, peas, beans and many other vegetable products
contain large quantities of it. Starch does not dissolve in
cold water; with hot water, it forms a paste.

254. Oxidation of Starch. — Under proper conditions,
starch can be oxidized to carbon dioxide and water. A
glance at the formula shows that the molecule contains
just enough oxygen to convert the hydrogen into water. We
need, therefore, twelve atoms of oxygen for the six carbon
atoms:

CeHioOe + 6O2 — ^ 6C0a + SHaO + 680,000 cal.

The great production of heat should be noticed. It is largely
by the oxidation of substances very similar to starch that
the heat of the animal body is maintained.

255. Source of the Energy of Life. — Plainly the equation
for the reduction of carbon dioxide to starch in the leaves of
plants must be the reverse of the one just given, and 680,000
cal. must be absorbed:

6CO2 + 5H2O — >- CeHioOs + 6O2 — 680,000 cal.

This 680,000 calories furnishes the energy for all the life
processes of animals and plants. Every process in the ani-
mal body occurs with a loss of energy, and this is true of
plant processes also, with the single exception just noted.
Just as the energy to run a clock is supplied only in the
wmding, so the energy which runs the life processes of or-
ganic nature is supplied solely by the reduction of carbon
dioxide by plants. We may well call this the most important
of all chemical processes.

Since the reduction does not take place in the dark, it is
clear that the energy must be absorbed from sunlight Ex-
periments made by growing plants imder variously colored
transparent screens have shown that it is mainly the yellow
rays in the neighborhood of the green that produce the effect.
It is a curious fact that these same rays are also the most
effective in acting upon the retina in the production of vision.

STARCH, GLUCOSE AND FRUCTOSE 193

256. Extraction and Uses of Starch. — Starch is extracted
chiefly from potatoes ixx Europe and from com in the United
States. The com is softened by soaking it in water into
which sulphur dioxide has been passed, and is then crushed.
The pulp is placed upon a movable sieve of fine brass gauze
and shaken imder a spray of water. The starch granules pass
through the sieve into a vat where the milky Uquid is allowed
to settle. A second filtration through fine silk gauze is
necessary to remove plant fibres, which pass through the
first sieve. Starch is used for laundry purposes, for making
paste, for sizing, for the manufacture of glucose, etc.

257. Glucose. — When starch is boiled with very weak
hydrochloric acid, it combines with a molecule of water and
passes into grape sugar or glucoscy CeHwOe. The action of
the hydrochloric acid is catalytic,

CeHioOs + H2O > C6H12O6

The hydrochloric acid — which would give the product a
sour taste — ^is repaoved by adding the proper quantity of
soda, which, as we shall see later, interacts with the hydro-
chloric acid, forming common salt, which, in small quantity,
does not damage the product. The solution of glucose ob-
tained in this way is a sweet, syrupy, yellowish liquid much
used as a table-syrup, for the manufacture of candy, and as a
substitute for malt in brewing.

Pure glucose is a white solid, very soluble in water. It be-
longs to a class of substances known as sugars, of which
table sugar is the most familiar example. Glucose is sweet,
but not as sweet as common sugar, and it does not crystallize
as readily. Glucose is contained in the juices of most sweet
fruits, for instance cherries and grapes. The sweet white
incrustation, which often appears on raisins, is glucose.

258. Fruit Sugar or Fructose. — Grape sugar is usually ac-
companied in fruits by another sugar called fruit sugar, or
fructose. The two sugars have exactly the same composition,
C6H12O6, but they differ in properties because the atoms are

194 AN INDUCTIVE CHEMISTRY

differently arranged. Fruit sugar is less soluble in water and
much sweeter than grape sugar. Like the latter, it is white
and crystalline.

259. Sucrose* — Common sugar^ called cane sugar or
sucrose, is one of the most important of all chemical prod-
ucts. Six million tons of it are obtained each year in
Europe from the sugar beet, which is a variety of the common
beet. Ordinary beets contain five per cent of sucrose, but
in the sugar beet the quantity has been increased by cultiva-
tion to twenty per cent and has even reached twenty-seven
per cent in certain specimens. It thrives in temperate re-
gions with abundant simlight. Germany, Austria, France
and Russia are the chief producers of beet sugar, but the in-
dustry is growing in the United States.

The srigar cane is a species of grass which reaches a height
of 2 to 6 meters and contains about twenty per cent of
sucrose. It grows only in warm climates. Nearly nine
million tons of sugar are obtained from it each year, chiefly in
Louisiana, Texas, South America, Hawaii, and the East and
West Indies, especially Cuba.

260. Extraction of Sugar. — ^In the extraction of sugar the cane is
passed between heavy iron rolls which squeeze out the juice. This
is boiled down in a closed vessel in the upper part of which a vacuum is
maintained so that the boiling-point is only about 65^. The crystals
which separate are dried in centrifugal machines. This brown impure
"raw sugar" is shipped to the refinery, where it is dissolved and the
sjrrup filtered through cloth bags to remove dust, plant fibre, etc., and
then through layers of bone black to remove the coloring matter.

Bone black is charcoal made from bones. It contains only about ten
per cent of carbon, the rest being the mineral matter of the bone, but
it has a remarkable power of absorbing coloring matters from liquids.

When the S3rrup leaves the bone black filters, it is colorless. It is
then boiled down in vacuum pans and dried in centrifugal machines.
The dr3dng of "granulated sugar'* is completed in a steam-heated cylin-
der, kept in motion to prevent the crystals sticking together. A trace of
ultramarine is added to the sugar to correct a yellow tint due to im-
purities.

The extraction of sugar from the beet is begim by cutting it into
thin slices which are systematically treated with water to dissolve the

SUGAR 195

sucrose. The purification of the beet-sugar is more complex than that
of cane sugar, because the impurities occmring with it in the beet are
more difficult to remove.

261. Properties of Sugar. — Sucrose crystallizes in color-
less inclined prisms which are seen in almost pure condition
in "rock candy." Sugar, salt and starch ("com starch")
are the only food products which are practically pure chemi-
cal compounds. Most foods are highly complex mixtiu'es.

Sugar is very soluble in water, and, when the solution is
boiled, the sucrose slowly takes up a molecule of water and
passes into a mixtiu*e of equal parts of grape sugar and fruit
sugar:

C12I122O11 -|- I12O — ^ Celii206 "h C6I112O6.
Sucrose Glucose Fructose

This change becomes rapid in presence of traces of hydro-
chloric a^id and other acids, which act catalytically. Syrup
obtained in this way is used in candy making and for imi-
tating honey. When it is mixed with 25% of real honey, it
is difficult for the chemist to distinguish the mixtiu^e from the
piu-e product of the bee-hive.

262. Carbohydrates. — Let us review the formulas of the
compounds thus far studied in the present chapter:

Starch CeHioOs

Glucose C6Hi20«

Fructose C6Hi20«

Sucrose C12H22O11

It will be noted that these four substances all contain
twice as many hydrogen atoms as they do oxygen atoms:
that is, they contain hydrogen and oxygen in the propor-
tions in which these two elements exist in water, H2O.
A compound contaming hydrogen and oxygen m these
proportions, imited to carbon, is called a carbohydrate.
Carbohydrates occur in animals, but they are especially
characteristic of plants.

196

AN INDUCTIVE CHEMISTRY

FiQ. 73. — ^Fermentation.

263. Cellulose. — The most abundant carbohydrate is
ceUulose, C6H10O6. The formula is the same as that of
starch, but it should be noted that in both substances
the molecular weight is unknown; the formula is
merely the simplest one which will express the com-
positioh.

Plant fiber and wood fiber are chiefly cellulose. Linen,
cotton, wood and paper consist mainly of it. The best

grades of filter paper are

^ ll ^^^ly P^^ cellulose. Pure

J^L cellulose is a soft white mass

of fibers, insoluble in most
liquids. Enormous quantities
of cellulose are made from
wood, for the manufacture of
cheaper grades of paper. The
wood, cut into small pieces, is
heated in a closed vessel imder
pressure for several days with a liquid which dissolves
the cement which holds the wood fibers together, but
does not affect the cellulose. Paper containing much
wood-fiber slowly turns brown, especially under the m-
fluence of light. The better papers are made of cotton or
linen rags.

264. Fermentation. — The fresh juice of grapes is sweet, on
account of the presence of grape sugar. Heated and sealed
up while hot, grape-juice remains sweet, but when kept with-
out heating, it enters into fermentation. Countless gas bub-
bles escape and the sweet taste is replaced by the alcoholic
flavor of wine. Examination of the liquid at this stage
shows that it contains innmnerable cells of a microscopic
plant called yeast.

Further information can be gained by the apparatus
of Fig. 73. The liquid contains about 100 grams of
glucose, dissolved in a liter of water. A yeast cake,
crushed in a little water, has been added. The small bottle

ALCOHOL 197

contains limewater. The U-tube is filled with frag-
ments of caustic soda to keep out the carbon dioxide
of the air. The experiment proceeds most rapidly at
about 30\

The white solid which appears in the limewater proves
that the gas, which escapes from the fermenting liquid, is
carbon dioxide. The alcohol which remains in the large
bottle can be separated by fractional distillation. Alcohol
boils at a lower temperatiu-e (78°.5) than water. Therefore,
when a mixture of alcohol and water is distilled, most of
the alcohol is contained in the earUer portions which are
collected.

Thus, if we distill 100 c.c. of the mixture, the distillate
(as the liquid obtained by condensing the vapor is called)
may contain enough alcohol to identify it by the taste and
smell. Or, we can put the 100 c.c. into a small flask and dis-
till 5 c.c. of it, and this second distillate will probably be rich
enough in alcohol to bum.

The equation for the fermentation of glucose is:

CeHiaOe — >■ 2C2H6O + 2CO2.
Glucose Alcohol

Fructose ferments in exactly the same way, the equation being
identical. Cane sugar does not ferment directly, but the yeast contains
a substance called invertasef which acts just as hydrochloric acid does
upon the sucrose (p. 195), converting it into glucose and fructose, which
then ferment.

265. Alcohol. — Alcohol f C2H6O, is a colorless liquid with a

pleasant odor and a burning taste. Its specific gravity is

0.8. It freezes at -130° to a white mass. It mixes with

water in all proportions, not forming two layers. Alcohol

takes fire readily and bums with a blue flame. When it is

burned in a cold dry bottle, water condenses in the walls and

carbon dioxide can be recognized by the limewater test.

Alcohol is used for making varnishes, lacquers, and important

drugs, like chloroform, chloral and iodoform. Alcohol

lamps with a mantle attached are employed in Europe
14

198 AN INDUCTIVE CHEMISTRY

for lighting. Pure alcohol is a violent poison. Dilute
solutions (alcoholic beverages) are injurious but the effects
are not so immediate.

266. Denatured Alcohol. — ^Although it costs only about
thirty cents to make a gallon of alcohol, yet the price at which
it sells is about ten times as much. The reason is that the
government exacts a tax which amounts to about $2.07 per
gallon. Alcohol intended, not for the production of bever-
ages, but for the mdustries which require it, is denatured, that
is, mixed with substances which give it a disgustmg taste or
render it more poisonous. Such alcohol is tax-free. The
substances most frequently used to denature alcohol in the
United States are 10% of wood alcohol and 0.5% of benzene.
Since wood alcohol is excessively poisonous — being especially
destructive in its action upon the eyes — denatured alcohol
must not be employed m the preparation of anything which is
to be taken internally, nor should it be used for bathing the
body.

267. Diastase. — The starch which is stored up in seeds
like wheat, rye and barley, acts as a supply of nourishment for
the young plant until it is able to provide for itself. Now it
is clear that the starch must be changed into something else
before it can serve as plant food, for starch does not dissolve
in watery Uquids, Uke plant sap. It would remain mert in
the roots, and could no more supply the stem and leaves of
the young plant with carbon than could so much charcoal-
powder. Nature solves this problem by the formation, dur-
ing the sprouting of seeds, of a substance called didstase,
which acts catalytically upon the starch and changes it to a
sugar called maltosey which has the same composition as
common sugar:

2C6H10O5 + H2O — >- C12H22O11.
Starch Maltose

268. Maltose. — Maltosey C12H22O11, is not as sweet as
sucrose. Like the latter, it dissolves freely in water and it

ALCOHOL 199

can therefore be carried about in the plant juices and used
where it is needed. Yeast transforms it to glucpse and fer-
ments the latter.

269. Malt LiquorSi Beer, Ale and Stout — Malt is made by
moistening selected barley and allowing it to form a sprout
nearly as long as the grain. The young plant is then killed by
a gentle heat. When malt is crushed, and treated with warm
water, the diastase rapidly changes the starch to maltose. The
liquid is then boiled with hops to give flavor and keeping
qualities.

After rapid cooling, the liquid is ready for fermentation. Pure
yeast is added to it in vats of great capacity, made of oak. The yeast
changes the maltose to glucose, which then ferments:

C6H12O6 — >■ 2C2H6O H- 2CX)2 + 35,000 cal.

The large evolution of heat makes it necessary to cool the vats, for in
the fermenting of beer the temperature must not be allowed to rise
above 5°. Brewing on a large scale only became possible with the
invention of the ice-machine.

In the fermentation of beer the yeast grows at the bottom of the
liquid and the finished product contains 3 to 5% of alcohol.^

In the manufacture of stout and porter a portion of the malt is heated
hot enough to char it a little and produce brown coloring matters, which
dissolve in the liquid.

Ale is fermented by a yeast which grows at the top of the liquid and
requires a temperature near that of an ordinary room (15®-22®). Ale
contains more alcohol than beer (up to 8%).^

270. Whiskey. — In the making of whiskey j rye or com is crushed and
heated gently with malt and water. The diastase converts the starch
of both malt and rye into maltose which is then fermented by the addi-
tion of pure yeast. Fermentation stops before the liquid contains 17%
of alcohol, for the yeast plant cannot work in strongly alcoholic liquids.
The liquid is then subjected to fractional distillation, carried out in such
a way that the distillate contains about 50% of alcohol by volume, the
balance being chiefly water with small quantities of flavoring sub-
stances.

271. Production of Alcohol. — The production of alcohol is carried out
in the same way, the chief differences being (1) that any cheap material
rich in starch can be used (potatoes or com), and (2) that distilling ap-
paratus of such perfection is employed that it is possible to obtain 95%

* Percentages of alcohol sire stated by volume.

200

AN INDUCTIVE CHEMISTRY

alcohol as a distillate. A diagram will make the matter clear and give
an idea of the quantities employed.

100 kilos potatoes containing 20% starch 3 kilos barley

steamed and crushed malted

4.5 kilos malt

Potato-pulp with malt
starch changed to maltose at 60*^

Yeast added
Fermented

Liquid containing 17% alcohol
DistiUed

Carbon dioxide
about 9 kilos (4.6 cubic meters)

12 liters alcohol

150 Uters distiUers' "swiU"
Used as cattle-food.

272. Relation of Yeast to Fermentation. — ^When yeast cells are
killed, their fermenting power is not destroyed. Thus, if yeast is
dipped into a mixture of alcohol and ether, the cells are killed, for they
will neither grow nor reproduce, but the dead yeast, when added to a
glucose-solution, wUl cause rapid fermentation. When living yeast is
ground with sharp sand, the cell walls are broken and the inside liquid
escapes. By proper filtration, the liquid can be freed from yeast-cells.
This sterilized liquid vigorously ferments glucose. These facts show
that fermentation is not connected in any way with the life of the
yeast plant. The part played by the cell is merely to produce and
to store up a substance which acts catal3rtically upon the glucose,
transforming it into alcohol and carbon dioxide. The name zymase
has been given to this substance. It is white and soluble in water,
but has not yet been obtained in pure condition.

273. Aldehyde. — Crude alcohol before it is purified by re-
distillation contains small quantities of aldehyde^ CsHiOL

VINEGAR 201

Pure aldehyde is a colorless liquid with a sharp odor, recall-
ing that of apples. It can be made by cautiously heating
alcohol with various mixtures which give off oxygen:

CzHeO + — ^ C,H40 + H2O.

Alcohol Aldehyde

274. The Formation of Vinegar. — When the bung is re-
moved from a cask of wine, so that air has access, the liquid
slowly turns to vinegar. Comparing the properties of
wine with those of vinegar, we can reach the conclusion
that the alcohol has been changed into an acid (we shall
learn something about the properties of acids pres-
ently). In fact, vinegar does contain from 5 to 15%
of acetic add.

While the change of wine to vinegar is going on, the liquid
contains great numbers of microscopic organisms called
ascetic add hacteriay which change the alcohol to acetic acid,
just as the yeast cells change glucose to alcohol.

Since the formation of vinegar requires the admission of
air, we might conclude that the alcohol is oxidized to
acetic acid. If so, the change ought to proceed rapidly
when the air has freer access. This is the basis of the
quick vinegar process, by means of which wine, or any
other dilute alcohol, can be transformed into vinegar in
a few hours.

A large cask, perforated with many holes to admit air, is packed with
beechwood shavings, which are moistened with vinegar to infect them
with the bacteria. Dilute alcohol, allowed to drip slowly through the
shavings, is completely converted into vinegar in a very short time.

275. Acetic Acid. — Acetic add, C2H4O2, is a colorless
liquid, which freezes, a little below room temperature, to an
ice-like solid. It smells like vinegar and, when diluted
with water, tastes like it. In contact with iron, zinc,
magnesium and some other metals, it liberates hydrogen.
It slowly converts dissolved cane sugar into glucose
and fructose.

202 AN INDUCTIVE CHEMISTRY

LUmua is a blue dye, obtained from a kind of moss. It
dissolves in water and, when a drop of acetic acid is added to
the blue liquid, the color at once changes to red.

276. Acids. — The statements just made are true not only
of acetic acid but of other acids also. Thus we may define
an acid as a substance having the following properties:

1. Its dilute water solution tastes sour,

2. It turns blue litmus solution red.

3. It converts cane sugar into glucose and fructose. Adwe acids,
like hydrochloric acid, produce this change rapidly; iruuiive acids, like
acetic acid, more slowly.

4. An acid is a hydrogen compoimd. Part or all of its hydrogen
escapes when the water solution of the acid is treated with a metal like
iron, zinc or magn^um. Other things being the same, the more active
the acid, the more rapidly the hydrogen is evolved.

Acetic acid, in the dilute form of wine-vinegar, wais the
only acid known to the ancients. The so-called "mineral"
aeids, hydrochloric, sulphuric and nitric, were prepared by the
alchemists during the middle ages.

277. Methyl Alcohol. — Methyl alcohol, CH4O, is called
wood alcohol because it is obtained by the distillation of
wood (p. 41). It is purified by fractional distillation. It
can be made from methane, but the method is not suitable for
practical purposes. Pure methyl alcohol is a liquid resem-
bling ordinary (ethyl) alcohol in appearance and odor. It
boils at a lower temperature (66**). Its intense poisonous ac-
tion has been referred to. When the quantity taken is too
small to kill, it often produces total blindness.

Wood alcohol is used in making varnish, in the manufac-
ture of dyes, in denaturing alcohol and in the manufacture of
formaldehyde.

278. Formaldehyde. — Formaldehyde, CH2O, is formed
when a mixture of the vapor of methyl alcohol with air is
passed over a hot spiral of copper wire:

CH4O + — ^ CH2O + H2O.

It is a colorless gas with a penetrating, unpleasant odor. It

SERIES OF CARBON COMPOUNDS 203

is sold as a 40% solution in water under the name formalin.
Formaldehyde is an excellent disinfectant, being rapidly
fatal to all kinds of micro-organisms. It does not tarnish
metal objects, nor bleach colored fabrics. It is almost the
only, disinfectant employed at present for fumigating rooms,
clothing, furniture, etc. When added to milk, meat and
other food products, formaldehyde prevents decay. Food
preserved in this way is unwholesome and the use of formal-
dehyde, as a food preservative, is illegal.

279. Formic Acid. — Formic acid, CH2O2 is a colorless liquid
with an uritatmg odor. It boils at 100^ It owes its name
to its presence in ants (Latin, formica). It is also contained
in the stmgmg hairs of the nettle.

When formic acid is allowed to drop into warm sulphuric
acid, pure carbon monoxide escapes.

CH2O2 — ^ H2O + CO.

The sulphuric acid retains the water. This is the best
laboratory method of making carbon monoxide.

Formic acid, owing to a new method of making it, has be-
come cheap, and is being used instead of acetic acid in
calico-printing and dyeing.

280. Series of Alcohols, Aldehydes and Acids. — Methyl
alcohol is the first member of a series of alcohols. Ordinary
(ethyl) alcohol is the second member. The general formula
of the series is CnH2n + 2O. Each member differs from the
one below by the addition of one carbon and two hydrogen
atoms (CH2).

CH4O methyl alcohol
C2H6O ethyl alcohol
CsHsO propyl alcohol, etc.

There is also a series of aldehydes, the general formula of
which is CnH2nO

C H2O formaldehyde
C2H4O ordinary aldehyde
CsHbO propyl aldehyde, etc.

204 AN INDUCTIVE CHEMISTRY

Finally, there is a series of acids, the general fonnula of
which is CnH2n02:

CH2O2 formic acid
C2H4O2 acetic acid
C8H6O2 propionic acid
C4H8O2 butyric acid

C16H32O2 palmitic acid
C18H86O2 stearic acid, etc.

Butyric acid gives the odor to rancid butter. Palmitic and
stearic acids are important constituents of animal and vege-
table fats and oils.

Definitions

Carbohydrate, A compound of carbon, hydrogen and oxygen, in
which there are twice as many hydrogen atoms as oxygen atoms.

Fermentation, The change of a sugar to alcohol and carbon
dioxide under the influence of yeast. In a general sense, the word
applies to all chemical changes brought about by microorganisms.

Add. A hydrogen compound which tastes sour, reddens blue
litmus, converts cane sugar into glucose and fructose, and, when it
interacts with metals like zinc or iron, Uberates hydrogen.

BOOK IV

THE SODIUM GROUP OF ELEMENTS.— THE

CHLORINE GROUP

INTRODUCTION

In Book IV we shall continue the plan we have followed
thus far, of devoting our main attention to compounds con-
taining only two elements. The starting-point of the work
will be the salt of the household, which we shall prove, by-
laboratory and lecture-table experiments, to be a compoimd
of a green suffocating gas called chlorine with a soft white
metal sodium.

The natural continuation of our work with salt will be a
study of the compounds of chlorine with the metals and non-
metals with which we are already familiar from the first three
books. These compounds are known as chlorides and many
of them are of decided scientific and commercial importance.

Turning to the chlorides of elements new to us, we shall
take up a mineral called sylvite which is much like salt in
taste and other properties. We shall not be surprised,
therefore, to find that it is a compoimd of chlorine with a me-
tal called potassium which is so similar to sodium that the
compounds of the two can be profitably studied together.

The conclusion will be formed by the study of a group of
elements which are remarkably similar to chlorine in chemical
behavior.

205

CHAPTER XVI

TABLE-SALT: SODIUM AND CHLORINE

281. Rock Salt. — The salt of the household is a white
powder, which consists of cubical crystals. Natural salt,
called "rock salt'' or halite, is an abundant mineral and is
mined, especially in Gennany and Austria. It occurs mixed
with clay, gypsum and other substances, and must be puri-
fied for table use. Most of the impurities are insoluble
in water. The rock salt is dissolved and the impurities
allowed to settle. When the clear Uquid is drawn off and
evaporated in an iron vessel, a much purer grade of salt is
obtained.

282. Salt Wells. — In our own country, extensive deposits of salt exist
in New York, Ohio, Michigan, Kansas, Nevada and other states. The
United States produces more salt than any other country, but very little
of it is obtained by mining. It is chiefly made by boiling down the water
of bolt springSf which are abundant in the states just mentioned. When
these natural brines do not flow from the earth, they are obtained by
sinking wells and pumping. Often the brine is too poor in salt to be
boiled down profitably. Then a hole is drilled into the salt-bearing
rock, which always abounds in the locality, and the brine is run into
it. When saturated with salt, it is pumped out and evaporated. At
present, the evaporation is often done in large vacuum vessels, like those
used in the sugar-refineries. The wet mass obtained by evaporation is
fed in at the top of a large, inclined, revolving cylinder, heated by steam.
A dry powder of salt runs out at the lower end.

283. Sea Salt — In warm, dry regions, salt is obtained from sear
water by natiu*al evaporation. At Giraud, near the mouth of the Rhone
in southern France, large shallow basins are dug in the clayey soil of the
strand of the Mediterranean. Sea-water is admitted in the Spring,
and allowed to evaporate until saturated with salt- Meanwhile, clay
and gypsum separate from it. The liquid is run into another basin,
where the evaporation is continued until much of the salt has deposited.
The crusts of salt are raked out and stood in heaps to drain. This salt
averages about 95% in purity. When the deposited salt begins to
be quite impure, the liquid is nm into a third basin, in which a lower
grade of salt is deposited.

206

TABLE SALT: SODIUM AND CHLORINE 207

The water of the open sea contains about 3.5% of solid matter of
which about 2.5% is salt. The remainder consists of a great variety
of substances. The water of some lakes is much richer in salt. The
Great Salt Lake contains over 20% of salt. In such waters, aquatic
life is impossible.

284. Salt Solution. — Salt dissolves in water. This means that, when
thrown into water, it disappears, slowly if the liquid is left to itself, and
rapidly if the vessel is shaken. A solid which behaves iij this way is
said to be soluble in water. The corresponding negative word is in-
soluble. The salt water obtained is caUed a solution. A solution may
be colored but it is dear. An insoluble solid, like starch-powder or clay,
can be dispersed through water by

shaking, but the mixture will be
turbidj like muddy water. A tur-
bid mixture of a solid and a liquid
is called a suspension. In time,
the suspended matter will settle,
leaving the liquid clear. Dissolved
matter never settles.

By slowly adding salt to a meas-
ured volume of water it can be
shown that there is a limit to the
quantity which the water will dis-
solve. 100 grams of water at 0°
will take up 35.7 grams of salt,
and no more. The solution is
then saturated and any more salt
thrown into it will simply fall to
the bottom and form a layer which,
no matter how thick, does not in-
crease the amount dissolved.

285. Effect of Heating on the
Amount of Salt Dissolved. — By

trsdng the same experiment at various temperatures it has been shown
that the quantity of salt taken up by 100 grams of water increases
slightly with rising temperature until, at 100°, nearly 40 grams of salt
are dissolved. The results are most easily understood from a "curve."
In Fig. 74 the distances measured from right to left indicate tempera-
tures, while the distances upward represent grams of the solid dis-
solved by 100 grams of water. The curve for salt shows at once the
slight but regular increase in solubility with rising temperature. The
steep ascent of the curve for nitre (saltpeter) shows strikingly the much
more rapid increase in the solubility of that substance.

150
140

130

120

100
00
80
70

60
50

rniT)

(xn~

3L»/*

yuiK

—

30
90

f 21

1' s

r 41

f 5

D° 61

r 81

r 8(

Fig. 74. — Solubility curves of salt and
nitre.

208 AN INDUCTIVE CHEMISTRY

A'most al solids are more soluble in hot water than in cold. There
are a few exceptions to this statement. Slaked lime and a few other
solids decrease in solubility when the temperature rises. This can be
illustrated by boiling some limewater, which at once becomes turbid
from the separation of some of the lime.

286. Application of the Idea of Concentration to Solutions. — It is
plain that solution is merely another example of the controlling influence
of concentration over chemical events. Pour water over sugar, and the
sugar dissolves until its concentration in the solution attains a certain
value. Then equilibrium results and no more sugar is taken up, even
if the two substances are left in contact for years.

Sugar (solid) -|- Water ^ ^ Syrup (saturated).

If the temperature is raised, more sugar is taken up, until its concen-
tration in the syrup attains a new value, higher than the old. Then
equilibrium again sets in, so long as the temperature remains the
same.

287. The Kinetic Point of View. — From the kinetic viewpoint, the
reasoning is almost like that ah^ady given for gas solutions (p. 71),
which should be re-read. We must think of sugar molecules escaping
from the surface of the solid and moving about among the water
molecules. At once sugar molecules begin to bombard the surface of the
solid sugar and the niunber which returns to the soUd state will increase
with the number of sugar molecules in each cubic centimeter of the syrup,
that is, with the concentration of the sugar. Throwing in more sugar
ha,s no effect, because, while we increase the opportunity of sugar
molecules to escape, we also increase the chance to return to exactly the
same extent.

That this is a fairly accurate picture of the real state of things is
proved by many facts, of which two may be stated. From the formulas
of sugar and water

C12H22O11 molecular weight 342
H2O molecular weight 18

we see that there can be no reasonable doubt that the sugar molecules
are larger and heavier than the water molecules. It follows that, to
a test of sufficient delicacy, sugar-solution ought to behave like water
with very fine solid particles suspended in it.

(1) When a beam of electric light is passed into pure water (free from
dust) in a dark room, the path of the beam is invisible. But when pure
sugar is dissolved in the pure water, the track of the beam of hght be-
comes visible, just as it is in water containing very fine dust. This
can only be due to the reflection of the light by the sugar molecules.

TABLE SALT: SODIUM AND CHLORINE 209

(2) Muddy water can be rapidly cleared by whirling it in a centrif-
ugal machine. The particles of mud, being vastly heavier than the
water molecules, go to the outside of the rotating vessel and collect there.
Now solutions behave in exactly the same way. It is necessary to
have a vessel divided into outer and inner compartments communi-
cating by small apertures — otherwise the liquid will mix uniformly
again as soon as the machine is stopped. When a solution is whirled
rapidly in a vessel of this kind, the dissolved substance collects pref-
erably in the outer compartmenty and even separates in the sohd state
there, if the whirling is rapid enough.

288. Supersaturated Solutions. — 100 c.c. of water at 100** dissolves
nearly 600 grams of sugar but at 20° only 200 grams. When a solution
of sugar which has been saturated at 100° is allowed to cool to 20°,
about three-fifths of the sugar separates in crystals.

Let us take 100 c.c. of water and saturate it with sugar at 20°. It will
take up 200 grams. We now heat the liquid to 100° and dissolve more
sugar in it. It would take up 300 grams additional, but we add only a
small fraction of this quantity, say 20 grams. The liquid is now cooled
to 20° once more. Now if this Hquid is kept quiet in a perfectly
clean bottle, the separation of the extra 20 grams of sugar may not occur
for a long time. Thus we have made a liquid which contains more sugar
than the aatwrated solution containSf at the same temperature. Such a
liquid is called a st^per-saturated solution. It can only exist so long as
the solid which tends to separate is absent. When a crystal of sugar is
let fall into our super-saturated solution, it at once drops the extra load
of 20 grams in crystals, and the saturated solution is formed.

289. Composition of Salt: Flame Test. — ^When a bit of
salt is held in the Bunsen flame by means of a clean iron wire
or a pair of forceps, the salt does not burn, but it vaporizes
and colors the flame intensely yellow. Many experiments
have shown that this yellow color is due to the presence of a
metal called sodium. Sodium itself and all its compounds
produce the color. Among familiar sodium compounds
which instantly color the flame bright yellow are soap,
washing soda, baking soda, caustic soda and borax.

290. Sodium. — Sodium, then, is one of the elements of
salt. It is a light metal, having about the same specific
gravity as water, and is soft enough to be easily cut with a
knife. The freshly cut surface has a bright, pinkish-white
metallic luster which disappears at once, for sodium rusts in

210 AN INDUCTIVE CHEMISTRY

the air far more rapidly than the ordinary metals. It is a
good conductor of the electric current and the high price
of copper has led to the proposal to use sodium — enclosed
in iron tubes — ^for the conduction of electric currents. As we
shall see, the iron is necessary to protect the sodium from
water and air. Sodium was first prepared by Sir Humphry
Davy m 1807.

Heated in the absence of air, sodium melts, at a little below
100°, to a liquid which looks like mercury. It boils at a red
heat, passing into a blue vapor, the specific gravity of which
shows that the sodium molecule contains bui one atom. This
seems to be the case with the molecules of all the metals.
The symbol of sodium is Na, from the German name
natrium.

Heated in air, sodium takes fire easily and bums with a
bright yellow flame to sodium oxide. In air which has been
carefully dried, it ignites with great difficulty — another in-
stance of the catalytic action of water vapor.

It is difficult to extract sodium from salt, and although salt
is the cheapest sodium compound, the sodium of the world
(about 5000 tons per year) is made from caustic soda by a
method we shall study later. Sodium is used in the prepara-
tion of dyes and other complex carbon compounds and espe-
cially in the manufacture of sodium cyanide, NaCN. Like
potassium cyanide, KCN, sodium cyanide is a white poison-
ous solid, very soluble in water. The solution dissolves gold
and is largely used in the cyanide process (p. 29).

291. Action of the Electric Current on Salt Water, — To
extract the other element of salt, we shall be obliged to resort
to the use of the electric current. A solution of one part of
salt in ten of water is placed in the apparatus indicated in
Fig. 75. The middle tube serves simply as a funnel to fill the
apparatus. Short pieces of platinum wire passing through
the glass carry the current to bits of platinum foil, through
which it enters and leaves the liquid. These pieces of foil
are called the electrodes. The foil at which the current

TABLE SALT: SODIUM AND CHLORINE 211

enters is the positive (+) electrode or anode, and the foil
where the current leaves the liquid is the negative ( — ) elec-
trode or cathode. The direct current of a dynamo is the
most convenient source of current, but an incandescent lamp
must be placed in the circuit to increase the resistance.
Apparatus in which carbon
rods take the place of the
platinum foil is often used
in this experiment, sincethe
platinum may be damaged.

The colorless gas which
appears at the cathode
proves, when we apply a
Bame, to be hydrogen. It
has nothing to do with the
salt, but arises from the l,
water by a decomposition
which does not interest us ^*\
at present. |3 \

The gas which collects 3^ '
at the anode is yellow-green

and suffocating. It does Fia. 75.— AbUoq ot the eleouio oumnt on

not take fire from a flame. *"

A piece of moist litmus paper held in it is bleached. This gas
is chlorine, the second element of salt. It collects more
slowly than the hydrogen because it is more soluble and
much of it is absorbed by the water.

292. Synthesis of Salt. — To complete our knowledge of
the chemical nature of salt, we must show that it contains
no third element. The simplest proof of this is the synthesis
of salt from sodium and chlorine.

Chlorine, generated in a flask, is passed over a bit of sodium
in a bulb, which is warmed with a Bunsen flame. The so-
dium bums with a dazzling yellow light. When cold, the
bulb can be broken, and will be found to contain a white
powder, which can be identified by tasting as salt.

212 AN INDUCTIVE CHEMISTRY

The black substance which coats the interior of the bulb is the ele-
ment silicoHf due to the reducing action of the sodiuni upon the glass.

Quantitative work shows that salt contains one atomic
weight of each of its elements. The symbol of chlorine is CI
and the equation for the synthesis of salt is:

Na + CI — >- NaCl + 98,000 cal.

The great evolution of heat explains the violence of the
change. The chemical name of salt is sodium chloride.

A second way to effect the synthesis of salt is to throw thin
shavings of sodium into a jar of chlorine, which is covered
and allowed to stand. The sodium slowly passes into a
white mass of salt. Exactly the same amount of heat is
evolved per gram of sodium as in the first method, but so
slowly that no noticeable rise in temperature results.

293. Chlorine, the Second Element of Salt. — The follow-
ing table gives some data about chlorine.

1 Occurrence: only in compounds. Salt is the most abimdant.

2 History: discovered by Scheele in 1774. Davy in 1809 proved

it to be an element.

3 Color: greenish-yellow.

4 Odor: suffocating.

5 Action on the body: dangerous irritation of the respiratory

passages.

6 Weight of one liter: 3.22 grams.

7 Critical Temperature: + 146^

8 Boiling-point of liquid: — 34"^.

9 Melting-point of solid: — 102''.

10 Solubility: 100 c.c. water at 20° dissolves 215 c.c.

1 1 Chemical character: intensely active. Even more so than

oxygen.

12 Uses: chiefly for bleaching paper and cotton; somewhat as a

disinfectant.

Since water dissolves more than twice its volume of
chlorine, the gas cannot be collected over water. Chlorine

TABLE SALT: SODIUM AND CHLORINE 213

is about 23^ times as heavy as air. Hence the tube from the
generator can be run into the bottom of an empty bottle.
The chlorine collects in the bottom and forces out the air at
the top. The color shows when the filling is complete.

The high critical temperature of chlorine indicates that it
is easy to liquefy it by pressure alone at ordinary tempera-
tures. Liquid chlorine in steel cylinders is now an article of
commerce.

Chlorine is chiefly made by the action of the electric cur-
rent upon salt-solution. In Germany potassium chloride,
KCl, is abundant, and is used instead of salt for the prepara-
tion of chlorine by the electric method.

294. Chemical Properties of Chlorine. — Chlorine, in pres-
ence of water vapor, converts all of the metals into their
chlorides. With the more active metals, like sodium, copper
and iron, the imion is rapid and the temperature may rise
high enough to make the products luminous. Inactive
metals, like gold and platinum, combine slowly with chlorine.

Most of these combinations fail to occur if the chlorine is carefully
dried. Thus sodium remains bright in dry chlorine for years, but if a
trace of water vapor is admitted, the formation of salt begins at once
and is soon complete. The reason that Gquid chlorine can be kept in
metal cylinders is that the water is removed during the liquefaction.

Chlorine combines with some of the non-metallic elements,
but there are others like nitrogen, carbon and oxygen which
are not affected by it. Chlorides of these elements can be
made by indirect methods. It is hardly necessary to add
that there are no chlorides of the inert elements of the argon
group.

Related Topics

295. Distinctions Between Suspensions and Solutions of

Solids. — The statements in the following table apply not

only to water, but also to other liquids. The freezing-points and

boiling-points in (6) and (7) must be those of the liquid under

consideration.
15

214

AN INDUCTIVE CHEMISTRY

Suspension

SoltUion

z Formatioii

Made by some external

Hastened by shak-

action, such as shaking

ing, but also formed

the sohd with the

spontaneoitsly from

hquid.

solid and hquid in
contact.

2 Appearance

Turbid

Clear

3 '^Keeping" qualities

Solid separates

Permanent

4 Effect of filtering

Solid retained by filter

Unchanged

5 Quantity of solid

No definite limit

Definite arnoimt at

taken up by loo c. c.

each temperature

of water

6 Freezing-point

0°, same as pure water

Always below 0**

7 Boilhig-point

100° same as pure water

Always above 100**

296. Solutions may be Solid, Liquid, or Gaseous. — There is
no reason for restricting solution to liquids. Many alloys
(p. 35) are solid solutions of the metals they contain. Rubber
absorbs large quantities of oxygen, carbon dioxide and other
gases forming solid solutions. Many kinds of candy are made
by melting the sugar, adding the other ingredients and letting
the mass cool to a solid solution without any separation. Glass
is another familiar solid solution. Air is an example of a
gaseous solution. A solution is best defined as a homogeneous
mixture of two or more substances and it may be liquid, solid, or
gaseous. But liquid solutions are easiest to make and handle
and are by far the most important.

Definitions

Solution, A uniform mixture of the molecules of two substances.

Soluble, Capable of entering into solution in a given liquid.

Insoluble, The negative corresponding to soluble.

" Curve. ^^ A line representing the solubility of a substance in
water at different temperatures. This method of plotting results
is widely used in science.

Saturated solution. A solution which has been shaken with a

TABLE SALT: SODIUM AND CHLORINE 215

solid until the solid ceases to dissolve because its concentration has
reached the limiting value.

Supersaturated solviion, A solution saturated at a higher tem-
perature and then cooled without the separation of any of the solid.
A solution which, when brought into contact with the solid which
has been dissolved in it, deposits crystals.

Flame test. The identification of a metal by means of the color
which its compounds give to the Bunsen flame.

Electrode, A piece of metal, or other conductor, through which
the electric current enters or leaves a solution.

Anode, The conductor through which the electric current enters
a solution; the positive electrode.

Cathode, The conductor through which the current leaves a sol-
ution ; the negative electrode.

Direct current. An electric current which flows continuously in
the same direction. An aUematin^ current flows back and forth,
changing its direction many times per second.

Suspension, A turbid mixture of two substances, usually a
solid and a liquid.

CHAPTER XVII
HYDROCHLORIC ACID

297. Combustion of Hydrogen in Chlorine. — ^When a jet
from which hydrogen is burning is lowered into a jar of
chlorine, the flame becomes large and pale. After the ex-
periment, the gas in the jar is colorless and has a sharp
caustic odor, different from that of chlorine, and
far less distressing. Blue Utmus paper placed in
it is not bleached, but reddened. This gas can be
nothing but a compound of hydrogen and chlorine.
For this reason it is called hydrogen chl(»ide.

398. Quantitative Experiment — ^The tube in Fig. 76 has
a stopcock which divides it into two portions, one of which
is just twice as long as the other. The short section is filled
with chlorine and the long one with hydrogen. Then the
stopcock is opened and the tube allowed to stand in a
well-lighted place.

Under the influence of light the two gases slowly unite ^
and since the color of the chlorine completely disappears, Fig. 76.—
we conclude that it has all combined with hydrogen. One ^sof^^ro^
end of the apparatus is now placed under mercury and gen chloride,
the glass stopper at that end removed. No gas escapes nor does any
mercury enter. This proves that the two gases combined without any
change in volume, that is, the volume of the hydrochloric acid is
simply the sum of the volumes of hydrogen and chlorine which have
united to form it.

The stopper is now re-inserted and the tube placed vertically
in a vessel of water, with the long section up. Hydrogen
chloride, although insoluble in mercury, is very soluble in water,
and, when the stopper at the lower end is withdrawn, the water
rises until the space left unfilled by it is equal to the volume
of the short section of the tube. The gas which remains
proves, upon the application of a flame, to be hydrogen. Since
we started with 2 volumes of hydrogen and 1 volume of chlo-

216

HYDROCHLORIC ACID

217

rine, and since one volume of hydrogen remains unused, it follows

that:

1 volume of hydrogen + 1 volume of chlorine

Or,

1 mole of hydrogen + 1 mole of chlorine

2 volumes of hydro-
gen chloride.

2 moles of hydrogen
chloride
22.4 Uters 22.4 liters 44.8 hters

We have seen that the mole of hydrogen contains two chemical unit
weights and that the formula of the gas is H2. The same is true of
chlorine. Its formula is CI2 (sec. 208).
Hence the equation is:

H2 + CI2 >- 2HC1.

From the molecular point of view, the argument is as follows:
According to Avogadro's h3rpothesis, the statement that

1 volume of
hydrogen

means that

1 molecule
of hydrogen

1 volume of
chlorine

2 volumes of
hydrogen chloride

1 molecule 2 molecules of

of chlorine hydrogen chloride.

Every molecule of hydrogen separates into two atoms, each of which
takes a chlorine atom as a partner and forms with it a molecule of hydro-
gen chloride. Every molecule of chlorine separates into two atoms,
each of which unites with a hydrogen atom:

H2 + CI2 >■ 2HC1.

299. Behavior of a Mixttire of Equal Volumes of Hydrogen
and Chlorine. — ^The behavior of a mixture of equal volumes
of hydrogen and chlorine, under varying illumination, is
stated in the following table:

1 Complete darkness.

2 Ordinary daylight.

3 Direct sunlight^ magnesium
light or arc light,

4 Direct application of flame
or electric spark.

5 Thermochemical equation

No combination.

Slow combination with a speed pro-
portional to the intensity of the light.
Instant combination with explosion,
but this does not occur if the mix-
ture is absolutely dry or very cold.
Explosion, less violent than in (3).

H2 + CI2 >■ 2HC1. + 52,000 cal.

218 AN INDUCTIVE CHEMISTRY

The attention of the student is called to the interesting
influence of light in (1), (2) and (3). He should re-read the
description of the formation of starch in plants (p. 191).
But there are two important distinctions to be noted here;

1. The formation of starch is accomplished chiefly by the
rays which most powerfully affect the eye, the yellow and
greenish yellow. These rays have little effect upon the pro-
duction of hydrogen chloride. The blue and violet rays are
the most active.

2. In the formation of starch, energy is absorbed from the
light, to be used afterward in running the life-processes of
plants and animals. But in the formation of hydrogen
chloride, energy is given out. The light merely starts the
combination just as a spark may start the explosion of gun-
powder, without contributing energy worth mentioning.

The student should notice also the catalytic action of water
vapor in (3). The great heat value in (5) explains the ex-
plosive character of the mixture and also the fact that hydro-
gen produces a flame when it imites quickly with chlorine.
Chlorine, when led into a jar of hydrogen, can also yield a
flame very similar to that of hydrogen burning in chlorine.

300. Properties of Hydrogen Chloride^ — The most impor-
tant properties of hydrogen chloride are as follows:

1 Appearance: colorless gas.

2 Weight of x liter: 1.63 grains.

3 Critical point: + 52''.

4 Boiling-point of liquid: —84''.

5 Melting-point of solid: —110''.

6 Solubility: 100 c.c. water dissolve 60,000 c.c. at 0**.

7 Solubility: 100 c.c. water dissolve 45,000 c.c. at 15".

8 Chemical conduct when dry: inactive.

9 Chemical conduct in presence of water: very active acid.

Owing to its high critical point, the gas can be liquefied by
pressure alone, but the liquid, on account of its low boiling-
point, cannot be kept in open vessels. The hydrochloric
acid of the laboratory is a saturated water solution, contain-
ing about 40% by weight of hydrogen chloride. When the

HYDROCHLORIC ACID 219

stopper of the laboratory bottle is removed, hydrogen
chloride escapes and produces, with the water vapor of the
air, a mist of little globules of hydrochloric acid; this causes
the fuming J which is more noticeable in damp weather.
301. Chemical Behavior of Hydrochloric Acid Solution. —
Hydrochloric acid solution is a good conductor of the elec-
tric current, has an intensely sour taste and, like all active
acids, is poisonous. It reddens blue litmus and rapidly
inverts sugar. It does not affect the precious (inactive) me-
tals, like gold and platinum, and has little or no action upon
silver, copper and mercury. Most other metals are rapidly
dissolved by it. Hydrogen escapes, and the chloride of the
metal dissolves and can be obtained by evaporating the
liquid:

Zn + 2HC1 — >• ZnCU + H,.

Zinc Zinc

chloride

In order to prove the correctness of this equation, one gram of ainc
can be dissolved in hydrochloric acid and the zinc chloride evaporated
to dryness and weighed. A simple calculation shows that one chemical
unit weight (65.5 grams) of zinc combines with two chemical unit
weights (35.5 X 2 = 71 grams) of chlorine. Confirmation is obtained
by measuring the hydrogen which escapes when a weighed quantity
of zinc is dissolved in hydrochloric acid. 65.5 grams of zinc liberate
22 . 4 liters of dry hydrogen at S.T.P., which is one mole or two chemical
unit weights of hydrogen (2.016 grams).

Magnesium behaves in the same way:

Mg + 2HC1 — >- MgCb + Ha

Magnesium
chloride

When a bit of sodium is thrown into concentrated hydro-
chloric acid, the metal melts to a sphere and runs about, his-
sing, on the surface. The hydrogen can be lighted with a
flame. A white powder itnade up of little cubes of salt falls
to the bottom.

Na + HCl — ^ NaCl + H.

These cases are quite different from the simple dissolving of solids
studied in the last chapter. When sugar dissolves in water the prin-

220 AN INDUCTIVE CHEMISTRY

ciple change is that the molecules of the sugar become widely separated.
The state of the sugar is much the same as if it had been changed to a
gas, occupying the same volume as the solution, and when the volume
is sufficiently reduced by evaporation, sugar separates, just as a gas
below its critical temperature condenses to a liquid when its volume is
sufficiently reduced by pressure.

But when zinc is placed in hydrochloric acid, it is not really the zinc
which dissolves. The metal is changed into zinc chloridcy which dis-
solves, and zinc chloride, not the original zinc, is obtained by evaporation.

Perfectly dry hydrogen chloride, whether liquid or gas,
fails to redden blue Utmus and has no action on the metals.
The same inactivity is noticed when the gas is dissolved in
some liquid other than water, like chloroform, benzene or
toluene. This striking difference in activity between the dry
substance and its water solution has been foimd also in many
other cases. The explanation comes later (Chap. XX).

302. The Deacon Process. — When hydrogen chloride is
heated with oxygen (air) chlorine is liberated:

2HC1 + :±^ H2O + CI2.

The interaction is slow, but in presence of cupric chloride
(CuCU) it becomes rapid enough to serve as the basis of a
practical method of making chlorine, called the Deacon
process. Bits of brick which have been dipped in cupric
chloride solution and dried are placed in a little tower and a
mixture of hydrochloric acid and air is heated to 400° and
passed through them. Since equilibrium results when 80%
of the hydrogen chloride is used up, the liberation of the
chlorine is incomplete — another instance of the influence of
concentration.

The reaction of the Deacon process is reversed when a
solution of chlorine in water is exposed to sunlight. Oxygen
escapes and hydrogen chloride dissolves:

H2O + CI2 -^ 2HC1 + 0.

303. Laboratory Method of Making Chlorine. — The Hbera-
tion of chlorine by oxidizing the hydrogen of hydrogen chlo-
ride to water is the basis of the method of making chlorine

HYDROCHLORIC ACID 221

given in the laboratory studies. Hydrochloric acid solution
is allowed to drop upon potassium permanganate, KMn04,
which is gently heated:

KMn04 + 8HC1 — ^ KCl + MnCt + 4H2O + 5C1.

Pyroludte liberates chlorine in the same way:

MnOa + 4HC1 — >■ MnCla + 2 H2O + CU.

It was by this last interaction that Scheele obtained chlorine
in 1774. This method is no longer used in the laboratory.

304. Action of Hydrochloric Acid on Oxides and Sul-
phides. — ^When zinc oxide dissolves in hydrochloric acid no
gas escapes, because the hydrogen of the acid forms water
with the oxygen of the oxide:

ZnO + 2HC1 — >■ ZnCla + H2O.

Many other oxides act similarly:

HgO + 2HC1 — >• HgCla + HjO.
Mercuric oxide

MgO + 2HC1 — >• MgCl2 + H2O.
Magnesium oxide

So far as the formation of the chlorides goes, these equations may be
proved in the laboratory. To prove the production of water, dry
hydrogen chloride may be passed over the dry oxide which is gently
heated. The metallic chloride remains, while drops of water condense
in the cooler part of the tube. Why are experiments with hydrogen
chloride solution valueless as proofs of the formation of water in these
interactions?

Hydrochloric acid has little or no action upon the sulphides
of mercury, copper and the precious metals. Upon many
other sulphides it acts in the same way as upon the cor-
responding oxides:

ZnS + 2HC1 — >■ ZnCl2 + H2S
Zinc blende
FeS + 2HC1 — ^ FeCl2 + H2S

Iron Ferrous

mono-sulphide chloride

The second interaction is the basis of the laboratory method

of making hydrogen sulphide.

222 AN INDUCTIVE CHEMISTRY

305. Decomposition of Hydrochloric Acid by Heat and
by the Electric Current. — Compounds which are formed from
their elements with much evolution of heat are stable. Hydro-
gen chloride is an instance. At 1800% which is far beyond
a white heat, the gas begins to decompose.

When the electric current passes through hydrochloric
acid solution, hydrogen escapes at the negative pole and
chlorine at the positive. The apparatus is the same as that
employed in decomposing salt (Fig. 75). Since some chlo-
rine dissolves in the water, the volume of chlorine is smaller
than that of hydrogen, especially at first. Later, when the
water becomes saturated with chlorine, there is an approach
to the equality of volumes which the equation demands:

2HC1 — ^ H2 + CI2.

A reference to sec. 299 will show that 52,000 cal. must be
absorbed in this process. Hence the need for a continiuma
supply of energy in the form of the electric current. The
decomposition ceases instantly when the current is inter-
rupted.

Dry hydrogen chloride (Uquid or gas) is a nOn-conductor.
So, also, are solutions of it in liquids like chloroform, benzene
and toluene. The student should notice that those forms of
hydrogen chloride which are chemically inactive are also non-
conductors. The explanation of this striking fact will be
given in Chap. XX.

306. Action of Sulphuric Acid on Salt. — When strong sul-
phuric acid, H2SO4, is poured over salt, a violent escape of
hydrogen chloride occurs, and sodium hydrogen sulphate,
NaHS04, remains:

NaCl -h H2SO4 — ^ NaHS04 + HCl.

On the contrary, when hydrochloric acid is added to a
solution of sodium hydrogen sulphate, sulphuric acid is
formed and a powder composed of little cubes of salt falls
to the bottom:

NaHS04 + HCl —>- NaCl + H2SO4.

HYDROCHLORIC ACID 223

Concentration always supplies an easy explanation of such cases.
When sulphuric acid is poured over salt, the hydrogen chloride escapes
and its concentration in the hquid is kept low. This prevents any in-
teraction between it and the sodium hydrogen sulphate formed.

Salt is nearly insoluble in concentrated hydrochloric acid. Hence,
when the latter is added to sodium hydrogen sulphate solution, the salt
separates in crystals, and its concentration in the liquid can not rise
much above zero. Therefore the inter-action between the salt and the
sulphuric ac d can not progress.

These experiments prove nothing regarding the relative activities of
the two acids. That hydrochloric acid is more active than sulphiu-ic is
shown by other methods, for instance by the fact that, under the same
circumstances, it inverts sugar more rapidly.

Hydrochloric acid is made on a large scale by the inter-
action of sulphuric acid and salt in iron pans. The gas is dis-
solved by passing it through large stoneware bottles contain-
ing water. Or, it is passed in at the bottom of a tower packed
with coke over which water trickles.

CHAPTER XVIII

VALENCE.— DETERMINATION OF ATOMIC WEIGHTS

307. Valence. — Following are the formulas of some hydro-
gen compomids:

I II III IV

Hydrochloric acid Water Ammonia Methane

HCl H2O NHs CH4

Hydrogen Sulphide
. H2S

An atom of chlorine is able to hold one atom of hydrogen in
combination to form a molecule. But an atom of oxygen
holds two hydrogen atoms; an atom of nitrogen, three; and
an atom of carbon, four. This has nothing to do with the
energy with which the elements unite. Chlorine imites
violently with hydrogen while carbon does so with great dif-
ficulty; yet the combining power of carbon is four times as
great as that of chlorine.

To the combining power of the atoms the name valence
has been given:

Chlorine in hydrogen chloride^ HCl, has a valence of 1, or is unioalerd,

Oxygen in ttJo/er, H2O, " " " 2, " bivalent,

Nitrogen in ammonia, NHi, ** " " 3, " trivalent.

Carbon in methane, CH4, " " " 4, " qiuidrivalent

We are not obliged to connect the notion of valence with the idea of
aUmis. There are always two ways of stating a thing of this kind.
We can just as well say that an atomic weight of chlorine (35. 5 grams) is
able to hold one atomic weight of hydrogen (1 . 008 gram) , while an atomic
weight of oxygen (16 grams) holds two, an atomic weight of nitrogen
(14 grams) three, and an atomic weight of carbon (12 grams) holds four
atomic weights of hydrogen.

308. Determination of Valence. — Since about two-thirds
of the elements, including most of the metals, seem to form
no hydrogen compoimds, their valence must be determined

224

VALENCE.— ATOMIC WEIGHTS 225

from their compounds with other elements. Thus, chlorine
combines with hydrogen atom to atom, and we conclude that,
the combining power of the chlorine atom is equal to that
of the hydrogen atom. This being the case, we can deter-
mine the valence of elements from the formulas of the chlor-
ides.

Zinc forms no hydrogen compoimd, but it forms a chloride,
ZnCU. Zinc, then, is bivalent. This conclusion is confirmed
by the study of other zinc compounds, for example:

Hydrogen Compound Zinc Compound

Water, H2O Zinc Oxide, ZnO

Hydrogen sulphide, H^S Zinc sulphide, ZnS

Sulphuric acid, H2SO4 Zinc sulphate, ZnS04

Nitric acid, HNOs Zinc nitrate Zn(N08)2

In each case the zinc atom takes the place of two hydrogen
atoms. This at once relieves the student of the labor of
memorizing the formulas of the zinc compoimds.

From the formula of salt, NaCl, it seems that sodium is
univalent. We can at once write the formulas of the four
sodium compounds correspondingto the hydrogen compoimds
in the above Ust, by simply substituting Na for each H.

Sodium oxide Na20

I Sodium sulphide NajS

Sodium sulphate Na2S04

Sodium nitrate NaNOs

What will be the formulas of the corresponding compounds of a trivalent
metal, e. g. aluminium?

309. The Value of Valence. — Valence is not a fact. It is an at-
tempt to arrange the facts of our science according to t|;^e idea of com-
bining power, just as books are classified in a library according to sub-
jects. Its chief value is to assist the student in becoming familiar with
the formulas of the compounds. It works well with some elements and
badly with others. Thus zinc is always bivalent and, if the student
grasps the meaning of this, he need pay no attention to the formulas of
the zinc compounds, for he can write them for himself. Carbon is
almost always quadrivalent and this is of great assistance in stud5dng
the countless compounds of the element. Silver is practically always
univalent, so the formulas of its compounds are like those of the cor-
responding compounds of hydrogen or of sodium.

226 AN INDUCTIVE CHEMISTRY

But to perceive that the method does not always work so smoothly,
we need only look at the formulas of three sulphur compounds:

1. Hydrogen sulphide H2S,

2. Sulphur dioxide SO2,

3. Sulphur trioxide S0|.

In (1) the sulphur is bivalent. Since oxygen is bivalent also, we might
expect the two elements to unite atom to atom, but no such compound
is known. Instead, we find that sulphur is quadrivalent in (2), while
in (3) it has a valence of six. As these instances show, the notion of
valence is of little use in dealing with the sulphur compounds. We are
obliged to study each compound separately, without the help of any
general principle. As a rule, however, it pays to remember the valence
of an element in studying its compounds. The exceptions can be noted
as they occur and they are usually not numerous enough to cause much
trouble. In the table in the appendix the valences of some of the com-
mon elements are given.

310. Illustration of the Way Atomic Weights are De-
termined. — On pages 84 to 88 the method of determining
atomic weights is taken up, using the oxides and sulphides
as a basis. These pages should be re-read.

Let us choose mercury as an example and start by assum-
ing that we know nothing about the atomic weight of the ele-
ment or the formulas of its compounds. A weighed quantity
of mercuric oxide is heated and all the mercury given oflf is
collected and weighed. The result shows that the standard
quantity of oxygen (16 grams) combines with 200 grams of
mercury. The method is so exact that the error in the final
result could hardly amoimt to 0.001 gram of mercury.

We do not know the formula of mercuric oxide. If it is
HgO, our result shows that the atomic weight of mercury is
200. But suppose the formula is Hg20. Then the 200 grams
of mercury we have obtained are two atomic weights, and
the atomic weight is ^f^ = 100. On the other hand, if the
formula of mercuric oxide is Hg02 then the 200 grams of
mercury which we have proved to combine with 16 grams of
oxygen is only half of an atomic weight of mercury and the
atomic weight is 200 X 2 = 400 grams. The analysis of
mercuric oxide shows us that the atomic weight of mercury

VALENCE.— ATOMIC WEIGHTS 227

is 200 or some multiple or fraction of 200, but it does not
show us which multiple or fraction to choose. In fact, until
about 1830 the formula of mercuric oxide was taken as
Hg02, and the atomic weight of mercury as 400.

311. Analysis of Mercuric Chloride. — Now let us analyze
mercuric chloride. A weighed, quantity is heated with pow-
dered lime, which combines with the chlorine. The mercury
which vaporizes is collected and weighed. The result shows
that the atomic weight of chlorine (35.5 grams) is combined
with 100 grams of mercury. Again we are confronted with
the same doubt. If the formula of mercuric chloride is HgCl,
the atomic weight of mercury is 100; the formula HgCU gives
200 and HgCU, 400. Since chlorine is univalent in its com-
pounds with the metals, we do not need to consider the possi-
bility of several atomic weights of mercury uniting with one
of chlorine.

312. The Mole of Mercuric Chloride. — The doubt can be
settled by ascertaining the mole (molecular weight) of mer-
curic chloride. The mole is the weight of 22 . 4 liters of the
vapor at S.T.P., that is, the weight of the vapor required
to fill our standard cube (p. 110).

Mercuric chloride is a solid at S.T.P. and we must weigh the vapor at
a higher temperature, say 546°. This is 546° + 273° = 819° absolute
temperature.

546° is chosen to simplify the calculation. Any temperature
above 300° (the boiling-point of mercuric chloride) can be used.

Since the volume of a mass of gas is proportional to its absolute tem-
perature, the standard volimie occupied by the moles of all gases at
S.T.P., 22.4 liters, becomes at 819° absolute:

819
22.4 X rrr = 22.4 X 3 = 67.2 liters.
273

The result shows that the weight of 67 . 2 liters of mercuric chloride
vapor at 546° is 271 grams.

The standard cube (22.4 liters) which holds the mole
(molecular weight) of all gases would hold 271 grams of mer-
curic chloride vapor, if the latter could exist at S.T.P. Of

228 AN INDUCTIVE CHEMISTRY

this quantity, our analysis shows that 200 grams must be mer-
cury and 71 grams chlorine. Two conclusions follow:

1. Mercuric chloride contains two atomic weights of
chlorine. Its formula is not HgCl or HgCU. Very likely
it is HgCU.

2. The atomic weight of mercury is not greater than 200.
The fact that we have found 200 parts of mercury in the
mole of one compound at once fixes 200 as the highest
possible value. But so far we have no proof that the
atomic weight is not a fraction of 200, 100 for example.
We have seen that this would make the formula of
mercuric oxide Hg20. In the same way, that of mercuric
chloride would be Hg2Cl2, for the 200 grams of mercury
in the mole would be two atomic weights. The mole
would still be 271.

313. The Mole of Mercury. — How, then, do we know that
200, not 100, is the correct value? This question is answered
by a wider study of the compounds of mercury. Many of them
have been vaporized and the weight of a liter of the vapor as-
certained. From this the weight of the vapor which would
fill the standard cube of 22.4 liters at S.T.P. has been cal-
culated. This fixes the value of the mole (molecular weight).
Now, in the mole of all these compounds, we always find 200
grams of mercury or some small multiple, never less than 200.
Hence 200 grams — ^not 100 — is the true atomic weight. We
must recall also the fact that for the vapor of mercury itself,
the mole is 200 (p. 160).

314. The Law of Dulong and Petit. — Further aid comes
from another quarter. About a century ago two French
chemists, Dulong and Petit, determined the specific heats
(p. 36) of a number of the elements. From these they
calculated the amoimt of heat required to warm the atomic
weight through 1^. Thus it requires 0.112 calorie to warm
one gram of iron through 1°. Since the atomic weight of
iron is 56, it will take 0.112 X 56 = 6.3 caJ. to warm the
atomic weight of iron 1 ^,

VALENCE.— ATOMIC WEIGHTS 229

Now it happens that the atomic weight of cadmium (112)
is twice that of iron. The specific heat of cadmium, deter-
mined by experiment, turns out to be 0.056, which is just
half that of iron. Hence the amoimt of heat required to
warm the atomic weight of cadmium 1° is 0.056 X 112 =
6.3 cal., which is identical with the result obtained for iron.
That this is not a mere accident is plain when the same cal-

culation is

made for other elements:

Name

Specific Heat

Atomic Weight

Product

Sodium

0.29

6.6

Zinc

0.096

65.5

6.3

Iiead

0.031

207

6.4

Mercury

0.032

200

6.4

,Gold

0.032

197

6.3

Silver

0.057

108

6.2

It is clear that the amount of heat required to warm the
atomic weight of these elements through 1 ** is nearly the same
for all, amounting to about 6.4 cal. We have

Specific heat X atomic weight = 6.4, or

64
atomic weight = '■

specific heat

Thus the analysis of mercuric oxide and of mercuric

chloride shows that the atomic weight of mercury is some

multiple or fraction of 200. The specific heat of mercury is

0.032.

64
Atomic weight = '- — = 200,

0.032

which shows at once that 200 is the correct atomic weight.

From the variation in the numbers under "product*' in the

table, it appears that the law of Dulong and Petit is not very

exact. This does not interfere with its use. The atomic

weight is really calculated from the chemical analysis,

which can be made as accurate as we please. The object

of the law of Dulong and Petit is merely to point out

which multiple to select. Thus, it indicates that the

atomic weight of mercury cannot be 100 or 400, but
16

230 AN INDUCTIVE CHEMISTRY

must be very close to 200, and this is all that is required
of it, for the exact value of the atomic weight can then
be calculated from the chemical analysis.

Related Topics

315. The Atomic Weight of Sulphur.— The methods which
may be employed in determing the atomic weight of sulphur are
good illustrations of the important principles we are now
studying.

On p. 94 we have discussed a method by which a weighed
quantity of sulphur can be burned, and the sulphur dioxide
weighed. We find that the weights of the two elements which
combine are equal, so that 16 grams of oxygen would unite with
16 grams of sulphur. It follows that the atomic weight of sul-
phur is some multiple or fraction of 16.

For some reason as yet unexplained, the law of Dulong and
Petit does not work as well with the non-metals as with the me-
tals. The specific heat of sulphur is 0.18.

0.18 X 16 = 2.9 cal., which is far below the usual value of
about 6 cal.

0.18 X 32 = 5.8, which is close enough to indicate that 32
is the correct figure.

We have seen that the atomic weight of mercury is 200. As-
sume that the formula of cinnabar, mercuric sulphide, is HgS.
Then the atomic weight of sulphur will be simply that quantity
which unites with 200 grams of mercury. The composition of
cinnabar is:

Mercury 86.21%

Sulphur 13.79%

86.21 : 13.79 : : 200 : a;

From which a; = 32 for the atomic weight of sulphur. On p.
86 we apphed a similar proportion to the composition of lead
sulphide with the same result.

A weighed quantity of silver powder can be changed, by heat-
ing in sulphur vapor, to silver sulphide (AgjS), which is weighed.
The result for the composition of silver sulphide is:

Silver 87.10%

Sulphur 12.90%

VALENCE.— ATOMIC WEIGHTS

231

If silver sulphide contains two atomic weights of silver
(Ag = 108) our proportion becomes

87.10 : 12.90 : : 216 : a; . . . x = 32.

These experiments are very exact and they show that the atomic
weight must be 32 or some multiple or fraction of 32. They do not
tell us which multiple to choose, for we have taken the formulas of
the sulphides for granted. So far the only fact bearing upon this
point is the specific heat, and that gives a doubtful answer. Just as
with mercury, the question is answered by determining the mole
(molecular weight) of a number of gaseous sulphur compounds.

Name

Weight of 22 A liters of

gas or vapor calculated

to S.T.P.

Stdphur in 22 A
liters

Sulphur dioxide
Sulphur trioxide
Hydrogen sulphide
Carbon disulphlde
Sulphur chloride

64 grams
80 grams
34.016 grams
76 grams
135 grams

32 grams
32 grams
32 grains
64 grams
64 grams

In the second column are the weights of the gases or vapors
required to fill the standard cube of 22.4 liters at S.T.P., while
the third column gives the sulphur contained in those weights.
Since no sulphur compound contains less than 32 grams of sul-
phur in 22 . 4 liters of its vapor, 32 is taken as the correct value
for the atomic weight. Carbon disulphlde, CSj, and sulphur
chloride, SjCU, contain two atomic weights of sulphur.

Oxygen is taken as the basis of the table of atomic weights be-
cause oxygen forms compounds with nearly all the other elements,
and the atomic weights, as we have seen, are often determined by
analyzing the oxides. The choice of i6 parts of oxygen by weight
as a standard is purely a matter of convenience. If a smaller
quantity than 16 parts was taken, elements like nitrogen, lithium
and hydrogen — whose atomic weights, under the present system,
are less than 16 — would have fractional atomic weights. Another
advantage of 16 parts of oxygen by weight as a standard is that
the atomic weight of hydrogen is close to unity, so close that, in
rough calculations, it can be taken as unity without serious error.

232 AN INDUCTIVE CHEMISTRY

Definitions

Valence, The combining power of the atom of an dement. The
valence of an atom is measured by the number of hydrogen atoms
it is able to hold in combination.

Univalent, Having the same combining power as hydrogen.

Bivalent, Having twice the combining power of hydrogen.

Trivalent, Having three times the combining power of hydrogen.

Quadrivalent, Having four times the combining power of
hydrogen.

CHAPTER XIX

IMPORTANT COMPOUNDS OF CHLORINE WITH THE
ELEMENTS ALREADY STUDIED

316. Chlorides of the Metals. — The folio wmg table
contains some information about the compomids of chlo-
rine with some of the metals. Notice the very small
solubiUty of silver chloride (1), equalling one part in 625,000
parts of water. Mercurous chloride dissolves to about the

Properties of Some Metallic Chlorides

Name

For-
mtUa

AgCl

Descrip-
tion

Melt-

ing

Point

260**

Boiling
Point

Grams Dis-

soloed by

100 ex.

Water {IS"")

Uses

I Silver

White

unknown

0.00016

Ebdsts insen-

chloride

curdy

sitive layer
of photo-
g r aphic
paper

2 Lead chlo-

PbCl2

White

447**

900**

None

ride

needles

3 Mercurous

HgCfc

White

none

sublimes

0.0002

Medicine

chloride

powder

4 Mercuric

HgCk

White

260**

300**

7.4

Dilute solu-

chloride

crystals

tion as dis-
infectant

5 Tindi-

SnCl2

White

250**

606**

270

Mordant in

chloride

crystals

dyeing

6 Zinc chlo-

ZnCb

White

100**

730**

300

Solution for

ride

crystals

cleaning
metals be-
fore solder-
ing, and as
an em-
balming
fluid

233

234 AN INDUCTIVE CHEMISTRY

same extent. Such substances are often said to be ''insoluble"
in water. Lead chloride is an example of sUght solubility,
while mercuric chloride is moderately soluble, and zinc
chloride very soluble. Mercurous chloride (3) is called
"calomel." When heated it sublimes; that is, it vaporizes
directly from the soUd state, without melting. It is a val-
uable medicine. Mercuric chloride (4) is called ''corrosive
sublimate." The dilute solution is much used for disinfect-
ing the surface of the body and the surgeon's hands
before operation. Mercuric chloride is poisonous. The
antidote is white of egg, or lai^ quantities of milk, taken
at once.

Especially in dyeing cotton, it is found that many colors
are not "fast," that is, they are washed out of the fabric by
water. But if the fabric is soaked in a solution of tin di-
chloride (5) before dyeing, it can then be dyed "fast." The
tin compound in the fabric forms an msoluble compound with
the dye. Substances which are used to fix dyes in this way
are called mordants. They are chiefly compoimds of tin,
aluminium, iron or chromium.

317. Some Non-metal Chlorides. — Since the non-metals
and their oxides are not affected by hydrochloric acid, their
chlorides are made by the direct union of the two elements,
or by other special methods.

Sulphur chloride^ S2CI2, is made by passing chlorine over
hot sulphur. It is a reddish yellow liquid with an un-
pleasant odor. It dissolves sulphur and is used in
vulcanizing rubber.

Chlorin^ does not combine directly with oxygen or nitrogen. Three
compoimds with oxygen and two with nitrogen have been prepared in-
directly. All five are endothermic and highly explosive. They can-
not be used for blasting, because they are so easily exploded by shock
that they cannot be transported or handled.

318. Action of Chlorine on Methane. — ^When a mixture of
chlorine with methane is exposed tp sunlight, the hydrogen
atoms of the methane are replaced by chlorine step by step.

IMPORTANT COMPOUNDS OF CHLORINE 235

The hydrogen unites with more chlorine, producing hydrogen
chloride:

CH4 + GI2 — >• CH3CI + HCl (1)

Meth;rl
chloride

GH3CI + CI2 — >• CH2CI2 + HCl (2)

Methylene
chloride

CH2CI2 + CI2 — >• CHCla + HCl (3)

Chloroform

^CHCIa + CI2 >• CCI4 + HCl (4)

Carbon
tetra-chloride

Methyl chloride j CH3CI, is a gas, which is compressed to a
liquid and sold in cylinders. It is used in the manufacture
of dyes.

Chloroform, CHCI3, is a heavy liquid with a pleasant odor.
It is used as an anaesthetic.

Carbon tetra-chloride , CCU, is a colorless liquid (specific
gravity 1.6). It is used in cleansing and scouring as a sub-
stitute for gasoline, over which it has the great advantage of
not being inflammable. Since it contains no hydrogen,
chlorine has no action upon it.

Chlorine acts in the same way upon other hydrocarbons.
The compounds produced are called substitution products, be-
cause the chlorine takes the place of the hydrogen. Other
non-metallic elements, like bromine (Chap. XXI) act in the
same way. Since there are many hydrocarbons, and since
substitution can take place in many ways, the total number of
substitution products is very great. They can be prepared
not only from the hydrocarbons, but also from other carbon
compounds. Thus methyl chloride, chloroform and carbon
tetra-chloride are not made practically from methane but by
other methods which, at present, are cheaper and more con-
venient for production on a large scale. However, the
invention of a suitable process is all that is needed to make
it very profitable to manufacture these substances from
methane. Natural gas would be a suitable raw material.

319. Sal-ammoniac. — Sal-ammoniac is a mineral which is

*.tt

236 AN INDUCTIVE CHEMISTRY

found as a white crust on lavas about Aetna, Vesuvius and
other volcanoes. It occurs sparingly, but is made artificially
in large quantities, for it has important applications. Its
use in filling batteries for door-bells and explosion-engines is
familiar to the student. Some of the facts concerning sal-
ammoniac are summarized below:

Appearance: small, white crystals.

Taste: sharp, salty.

Specific gravity: 1.5.

Behavior when heated: vaporizes without melting (see below).

Soluhillty: 100 c.c. water dissolves 37 grams at 20°, more at higher
temperatures. It dissolves with marked absorption of heat. The
solution has no effect on the color of red or blue litmus.

Uses: filling electric batteries; frequent ingredient in cough-mixtures
and cough-lozenges.

320. Chemical Nature of Sal-ammoniac. — No doubt the
student is aware of the fact that the sal-ammoniac in the

battery v^rhich rings the door-bell be-
comes exhausted and must be renew^ed
from time to time. He must have
noticed also that the zinc rods which
dip into the liquid become corroded.
It follows that zinc and sal-ammoniac
Fio. 77.— Synthesis of interact, but that the change is very
sal-ammoniac. gj^^ j^ike all chemical changes, it

is greatly quickened when the temperature is raised.

When a mixture of sal-ammoniac and zinc powder is heated in a test
tube, ammonia escapes and can be recognized by its odor. That some-
thing else is liberated in addition to the ammonia can be shown by col-
lecting the gas over water in the usual way. The ammonia is complete-
ly absorbed by the water, but a colorless gas collects, which proves, upon
the application of flame, to be hydrogen. The residue in the test tube
in which the mixtiu-e was heated contains zinc chloride, ZnCfe.

This experiment proves that sal-ammoniac contains nitrogen, hydro-
gen and chlorine. Quantitative information can be obtained by the
sjrnthesis of sal-ammoniac from ammonia and hydrogen chloride (Fig. 77).
10 c.c. of ammonia gas and 10 c.c. of hydrogen chloride are collected
in small measuring cylinders over mercury. The hydrogen chloride is
then allowed to pass up without loss through the mercury into the

IMPORTANT COMPOUNDS OF CHLORINE 237

ammonia. A white smoke is formed and the mercury rises. When the
combination is complete, it is found that both gases have disappeared.
The white solid in the cylinder proves to be sal-ammoniac.

The two gases have united volume to volume, which means
molecule to molecule. The simplest equation, therefore, is:

NH3 + HCl — ^ NH4CI.

The formula NH4CI requires a molecular weight of 53 . 5.
Now, when 53.5 grams of sal-ammoniac is vaporized, the
volume of the vapor, calculated to S.T.P., amounts to 44.8
Uters instead of the 22.4 we should expect. This caused
much discussion among chemists, imtil it was shown that,
when heated, the sal-ammoniac decomposes:

NH4CI — ^ NH, + HCl.

Since this doubles the number of molecules present, it
doubles the volume of the vapor. As soon as the vapor
cools, re-combination to sal-ammoniac takes place, so that
careful work is necessary to show that the sal-anmioniac has
ever been separated at all.

Decomposition of this sort, caused by heat and reversed by
cooling, is very common. It is called dissociation.

If the sal-ammoniac is free from every trace of water, it does not
dissociate when heated. In that case, 53 . 5 grams of the vapor occupy,
calculated to S.T.P., the normal volimie of 22 . 4 liters. It is interest-
ing, also, that perfectly dry ammonia can be mixed with perfectly
dry hydrogen chloride without the formation of any sal-ammoniac.

We can now write the equation for the interaction of sal-
ammoniac and zinc:

Zn + 2 NH4CI — >• ZnCla + 2 NH, + H2.

321. Ammonium Compounds. — Sal-ammoniac is similar
to the chlorides described in the table (p. 233). Its resem-
blance to salt is especially close. Like salt it often crys-
tallizes in cubes, its taste is similar, it is soluble in water to
about the same extent, it gives oflf hydrogen chloride when
treated with sulphuric acid, and so on. We should violate all

238

AN INDUCTIVE CHEMISTRY

the principles of good classification if we refused to call sal-
ammoniac a chloride,
A glance at the three formulas:

HCl

NaCl

NH4CI

shows that the part of the atom of hydrogen in hydrochloric
acid, and of the atom of sodium in table-6alt, is played, in sal-
ammoniac, by a group of five aioms, NH4. A molecule of sal-
ammoniac is composed of this group, united to an atom of
chlorine.

To the group NH4 the name ammonium is given. The
chemical name, then, of sal-ammoniac is ammonium chloride.

Corresponding to each of the sodium compounds is an ammoniiun
compound, in which the place of the sodiimi atom is taken by the group
NH4. We may illustrate by the most familiar and important three
compounds of both classes:

Adda
Hydrogen chloride

HCl
Nitric acid

HNO3
Sulphuric acid

H2SO4

Sodium Compounds
Sodium chloride

NaCl
Sodium nitrate

NaNOa
Sodium sulphate

Na2S04

Amm^mium Compounds
Ammonium chloride

NH4CI
Anunonium nitrate

NH4NO3
Ammoniiun sulphate

(NH4)2S04

It will be noted that ammonium (NH4) differs from
ammonia (NHs) by one atom of hydrogen. It also differs
from ammonia in the important respect that it is not a real
substance. No one has succeeded in obtaining ammonium by
itself. It is merely a group of atoms, which exists in the
molecules of a whole series of compounds, but never alone.

Such a group of atoms is called a radical. Another ex-
ample of a radical is methyl, CH3. There are many methyl
compounds:

Methyl oxide (CH3)20

Methyl sulphide (CH3)2S

Methyl chloride CH3CI

Methyl nitrate CH3NO3

Methyl sulphate (CH3)2SQ4

IMPORTANT COMPOUNDS OF CHLORINE 239

and hundreds of others. Like ammonium, methyl cannot
exist by itself. It will be noted that both radicals are univ-
alent.

Related Topics

322. Salts. — Some of the chlorides of the metals are described
in the table at the beginning of this chapter. There are many
others, for the hydrogen of hydrogen chloride can be replaced
by many metals. The metaUic chlorides which result are
called the salts of hydrochloric acid.

In the same way, there corresponds to nitric acid (HNO3) a
series of salts formed by the replacement of its hydrogen by
metals. Sodium nitrate (NaNO«) is an example. Sodium sul-
phate (Na2S04) is an example of the salts of sulphuric acid
(H,S04).

Table-salt, which has been known for ages, was the first
"salt," and the term was gradually extended to other sub-
stances which seemed to resemble it more or less. The salts
are crystalline solids, usually odoriess, less easily vaporized and
less active chemically than the corresponding acids. Their
water solutions conduct the electric current and, when nothing
but water and the salt are present^ do not affect the color of either
red or blue litmus. A re-inspection of the table of metallic
chlorides (p. 233) will show the great variation in properties
among the salts of the same acid.

Compounds in which the hydrogen of acids is replaced by
radicals are classed as salts when their properties require it,
otherwise not. We have just seen that all the properties of
ammonium chloride stamp it as a salt in which the hydrogen of
hydrochloric acid is replaced by ammonium.

In methyl chloride, CHtCl, the hydrogen of hydrochloric acid
is replaced by methyl, CHt, yet the following statement of its
properties will show that it would be absurd to regard
it as a salt: It is a gas with an ethereal odor. It does not
interact with sulphuric acid. It is slightly soluble in water;
the solution has no salty taste and does not conduct the
electric current.

For similar reasons, methyl nitrate, CHjNOj, and methyl
sulphate (CH2)tS04 cannot be regarded as salts of the corres-

240 AN INDUCTIVE CHEMISTRY

ponding acids. Such compounds are put into a class by them-
selves and are called esters.

Non-metallic chlorides, like sulphur chloride and carbon tetra-
chloride, have none of the properties of salts.

Definitions

SMime. To vaporize directly from the solid state, without
melting.

Mordant. A substance used in dyeing, not as a color, but to
make the dye adhere to the fabric.

Dissociationy Decomposition, caused by heat and reversed by
coohng.

Radicals A group of atoms found in the molecules of a whole
class of compounds.

SaUs. Compounds in which the hydrogen of acids is replaced
by metals or by radicals.

Esters. Compounds in which the hydrogen of acids is replaced
by radicals composed of carbon and hydrogen. Esters differ com-
pletdy from salts in properties.

CHAPTER XX

SYLVITE, POTASSIUM, CAUSTIC SODA AND CAUSTIC
POTASH.— SUGAR SOLUTION COMPARED WITH

SALT SOLUTION

323. Sylvite. — Sylvite is a mineral which is found at Stass-
furt and elsewhere in northern Germany. Its resemblance
to rock-salt is close, as will be seen from the following para-
graph and this suggests the probability of a close chemical
relationship between the two minerals.

When pure, sylvite forms colorless crystals, not cubical, but
readily breaking along the faces of a cube when struck. Its
taste is salty and bitter. At room-temperature, its solu-
bility in water is nearly the same as that of table-salt. Cold
water dissolves less sylvite than salt and hot water more;
that is, its solubility is more influenced by temperature than
that of salt. When the electric ciu-rent is passed through a
solution of sylvite, chlorine is set free at the anode and hydro-
gen (from the water) at the cathode, just as with table-salt.
Sylvite is therefore a chloride.

In the Bunsen flame, sylvite produces a delicate violet
color. This flame color is a proof of the presence of a metal
called potassiunty which is very similar to sodiimu

324. Properties of Potassium. — The following table gives
some data concerning potassium:

Appearance: silver-white metal, Hardness: softer than sodium,

tarnishes instantly in the air. easily cut with a knife.

Symbol: K (from German ''ICa- Atomic weight: 39.
Kum").

Specific Gravity: 0.86. Melting-point: 62**.5.

Chemical conduct: intensely ac- Boiling-point: 720*^: vapor is green

tive, even more so than sodium. and contains only one atom in

the molecule.

Uses: none.

241

242 AN INDUCTIVE CHEMISTRY

325. Sjmthesis of Sylvite. — In order to show that no
third element is present in sylvite, we may bum potassium in
chlorine, just as we did sodium (p. 211). There is an ener-
getic combustion, violet Hght being radiated, instead of
yellow. The white substance left in the bulb is identical
with powdered sylvite. Sylvite is therefore potassium
chloride. Quantitative work shows that its formula is
KCl. The combination of potassimn and chlorine may be
written thus:

K + CI — >• KCl + 106,000 caf.

Although the light display is less dazzling than in
the synthesis of table salt, the total energy evolved
is greater (p. 212). Nevertheless, a gram of sodiuni
burned in chlorine, gives more heat than a gram of
potassium. Why?

326. The Stassfurt Salts.— The city of Stassfurt (population 20,000)
is in North Germany, forty miles south of Magdeburg. Salt wells have
been worked there for centuries and this fact caused the Prussian gov-
ernment to undertake borings which, in 1843, penetrated into a bed of
rock-salt more than 1000 meters thick. Above this are layers con-
taining potassium chloride and potassium sulphate with other sub-
stances. These upper layers — often 100 meters or more thick — ^which
yielded no sodium chloride, were at first regarded as a mere nuisance.
They have proved to be the most valuable portion of the deposit.
Millions of tons of more or less impure potassium chloride and potas-
sium sulphate are obtained at Stassfurt yearly, some of which goes into
the chemical industries. Most of it, however, is used by farmers as a
fertilizer, for potassium compounds are indispensable to the growth of
plants.

Similar deposits have been detected by borings made at many other
places quite remote from Stassfurt, so that they must exist under great
areas of North Germany. Their total value to chemical industry and to
agriculture is beyond calculation. Some of the giant sea-weeds which
grow along the coast of California contains as much as 35 per cent of
their dry weight of potassium chloride. They also contain considerable
quantities of iodine.

327. Action of Sodium on Water. — ^We have seen that
sodium liberates hydrogen from hydrochloric acid (p. 219),

CAUSTIC SODA AND CAUSTIC POTASH 243

One atomic weight of sodium (23 grams) sets free one atomic
weight of hydrogen (1.008 grams):

Na + HCl —>- NaCl + H.

Sodium also liberates hydrogen violently from water.
When the metal is weighed, and the weight of the hydrogen
calculated from its volume, it is found that a fixed weight of
sodium sets free the same weight of hydrogen from water
as from hydrochloric acid. In either case:

Na (23 grams) yields H (1.008 gram).

The experiment is always carried out with a large excess of water,
so that the small but definite quantity of water which disappears by
interacting with the bit of sodium is not missed.

The liquid which remains has acquired a bitter taste and
feels soapy between the fingers. It turns red litmus paper
blue, reversing the color-change produced by acids. The
dissolved substance, which is responsible for these new prop-
erties, can be obtained by evaporation to dryness, when a
white solid remains, which is called caustic soda on account
of its corrosive action on animal and vegetable tissues and
on many metals.

That this caustic soda contains the sodium used can be
shown by holding a bit of it in the flame, when the strong
yellow color betrays the presence of the metal. That it
contains hydrogen can be proved by heating it with powdered
zinc and collecting the gas over water. With a fixed weight
of sodium, the weights of hydrogen liberated in the two ex-
periments (1) when the metal is treated directly with water,
(2) when the caustic soda is afterward heated with zinc
powder, are exactly the same. Sodium liberaies half the hydro-
gen from water; the other half remains in the caustic soda.

These results can be summed up in the equation:

Na + H2O — >- NaOH + H.

Caustic soda, NaOH, differs from the oxides in containing
hydrogen in addition to oxygen. Hence its chemical name,
sodium hydroxide.

244 AN INDUCTIYE CHEMISTRY

328. Sodium Hydroxide. — Sodium hydroxide, NaOH, is
often Bold for household putpoees in cans, under the name
"concentrated lye." The purer grades are sold in the form of
round sticks which are made by casting the melted substance.
It melts below a red heat and is very soluble in water. It
must be kept away from air, from which it rapidly atoorbs
water and carbon dioxide. It is a most important commer-
cial product, being used in great quantities
for the manufacture of soap and for other
chemical industries.

319. Prepaiation of Sodium Hrdttadds. — We

ara DOW in a poeitioB to undenrtand more full^

what h^ipens when the electrio current is passed

throu^ a solution of salt. Chlorine escapes

at the anode and hsrdrogeD from the water at

the cathode. Sodium hydroxide is formed at

the cathode and disBolvee in the water. Using

the apparatus of Fig. 75, this fact can be shown

by coloring the salt solution with a httle red

litmus. The Utmus will be bleached by the

. chlorine around the anode, and turned blue at

o( s^t ■olution. *''* cathode by the sodium hydroxide. We may

assume that sodium separates, for an instant, at

the cathode, and at once interacts with the water, liberating hydrogen

and forming sodium hydroxide.

Caustic soda is now made very lai^ely by the method indicated above.
The chief problem is to keep the chlorine away from the sodium hy-
droxide, for the two will interact if allowed to come together. In the
f^paratus of fig. 78 the layer of mercury m n prevents the chlorine
lil>erated at the anode A from craaing into contact with the
sodium hydroxide formed at the cathode C. In one form of
apparatus, used on a large scale, the vessel is divided into two
parts by a porous partition. The anode is in one chamber and
the cathode in the other. The chlorine is led away from the anode
chamber through a tube, and has no chance to interact with the
sodium hydroxide which is formed at the cathode. The partition
permits the ciureat to pass because it is porous, and is saturated
with salt solution.

Decomposition by the electric current is called electiolysla.

CAUSTIC SODA AND CAUSTIC POTASH 245

Fia. 79. — Preparation of
Bodium.

330. Potassium Bydroidde.— Potassium interacts with
water in the same way as sodium :

K + H2O — ^ KOH + H.

The action is more violent, so that the hydrogen ignites and
bums, with a flame colored violet by potassium vapor.
Potassium hydroxide is called caustic potash. It is very simi-
lar to caustic soda, and is made by
the same methods, using potassium
chloride instead of salt.

331. Manufacture of Sodium. —
When melted caustic soda is electro-
lyzed, oxygen is liberated at the anode,
and sodium and hydrogen at the
cathode. Caustic potash behaves in
a similar way. It was by this method
that Sir Humphry Davy, in 1807,
discovered sodium and potassium.

NaOH — ^ Na + O + H.

Sodium is now made on a large scale by Davy's process at Niagara
and elsewhere. Fig. 79 is a diagram of the apparatus devised by
Costner for this purpose. The caustic soda is contained in an iron
cylinder through the bottom of which the cathode C projects. Several
anodes A A surround the cathode. The sodium cdlects in a cylindrical
vessel V which is placed over the cathode. This serves to protect it
from the oxygen. The heat produced by the passage of the current
keeps the caustic soda melted. It is more difficult to make potassium
in this way on account of the tendency of the metal to bum as soon as
it is liberated. Since potassium has no important uses, little of it is
made.

332. Bases. — ^When hydrogen chloride is passed over a
little powdered caustic soda there is an energetic interaction;
water is formed and salt remains in the tube:

NaOH + HCl — ^ NaCl + H2O.

When solvMons of hydrochloric acid and sodium hydroxide
are mixed, the salt remains dissolved and can be obtained by
evaporation. The sodium hydroxide can be placed in a dish
17

246 AN INDUCTIVE CHEMISTRY

and colored blue with a drop of litmus. Dilute hydrochloric
acid is added from a burette, Fig. 80, which is a graduated
tube, with a stopcock at the bottom. The liquid remains
blue imtil all the sodium hydroxide is converted into salt.
At this point, a single additional drop of acid turns the liquid
red. If it is evaporated, salt is left and can be
identified by its taste. As we have seen, salt is
far less active than hydrochloric acid or caustic
soda, having, for instance, no effect on the color
of litmus, Uttle corrosive action on the metals
and no caustic action on organic matter.
Potassium hydroxide, which is so similar to
L|_| sodium hydroxide, interacts with hydrochloric
t acid in the same way:

KOH + HCl — ^ KCl + H2O.
We may also write the interactions of the two
hydroxides with nitric acid:

NaOH + HNO3 — >- NaNOs + H2O.

Sodium
nitrate

F1G.80.-A KOH + HNO3 —>- KNOs + H2O.

burette. Potaasium

nitrate

The hydroxides of potassium and sodium are types of an
important class of substances, the bases. A base is the
hydroxide of a metal. Soluble bases have a bitter taste,
quite imlike the sour taste of an acid. The color-changes pro-
duced by acids in sensitive dye-stuffs, like Utmus, are re-
versed by bases. Water solutions of bases, like those of
acids and salts conduct the electric current: solutions of active
bases and acids conduct welly those of inactive bases and
acids are poor conductors. When an acid and a base are
brought together, the OH of the base produces water with
the H of the acid and the residues of both molecules form
a salt. Because the peculiar properties of both acid and base
disappear, seeming to destroy each other, the term neutraliza-
tion is applied to the formation of a salt by their interaction.

J. H. tan't HOFP
. Holland, 1S52. D. 191L

CONDUCTIVITY OF SOLUTIONS 247

Related Topics

333. The Physical Properties of Solutions in Water. — A sim-
ple apparatus for finding out whether a water solution con-
ducts the current is shown in Fig. 81. The liquid to be tested
is placed in a beaker and the metal electrodes dipped into it.
The lamp interposes a resistance which cuts down the current to
a suitable strength, and, at the same time, indicates, by
lighting up more or less,
whether the liquid allows 4 " ^^ ^ !^ N
much or little current to
pass.

The results show that

solutions are of two very Fig. Sl.-Apparatus for testing the conducting

power of solutions.

different sorts:

1. There is a group which, to all intents and purposes, stops
the current altogether, for the lamp fails to light up. To this
class belong water solutions of cane sugar, glucose, fruit sugar,
glycerine, alcohol, ether, etc.

2. There is another group, the members of which conduct well
enough to make the lamp light up more or less brightly. To this
class belong water solutions of hydrochloric, nitric and acetic
acids, sodium and potassium hydroxides, and salt. In fact, it
includes water solutions of all acids, bases and salts. In order
to compare results, the solutions should be made so that the
strength, measured in moles per liter, is the same for all.

None of these solutions conduct nearly as well as a mass of
copper of the same size and shape, but they all conduct much
better than pure water. While the current passes, there is
evidence of chemical change at the electrodes, escape of gases or
separation of metals, as the case may be. That is to say,
electrolysis is taking place. Hence, the members of this second
group are called electrolytes. Acids, bases and salts are elec-
trolytes, other substances are not. The solution of an active
acid, like^ hydrochloric or nitric, allows the lamp to glow brightly,
while the solution of an inactive acid, like acetic, shows by the
feeble glow of the lamp, that it does not conduct as well. Active
and inactive bases show similar differences.

334. The Rise in the Boiling-Point. — We will now leave the
electrolytes, to return to them later, and devote ourselves to the

248 AN INDUCTIVE CHEMISTRY

nonconducting soltUions, which are much simpler in their be-
havior and easier to understand.

A solution of sugar boils at a higher temperature than water;
the sugar molecules attract the water molecules and make it
more difficult for them to leave the liquid and form vapor.
There ought, then, to be some connection between the concen-
tration of a sugar solution and the temperature at which it boils.

The plain way to get exact information is to dissolve weighed
quantities of sugar in a weighed quantity or a measured volume
of water (say 100 c.c. ^ 100 grams) and to measure the rise in
the boiling-point with a delicate thermometer, graduated in frac-
tions of a degree. The molecular weight of sugar (CuHuOn) is,
in round numbers, 342. We cannot well dissolve 342 grams of
sugar in 100 grams of water, for the solution would be a thick
syrup impossible to work with, but we can use a definite fraction,
say one-tenth of the molecular weight (34.2 grams). Dissolv-
ing this in 100 c.c. water, we note a rise in the boiling-point of
about one-half a degree, from 100** to 100*^.5. A second portion
of 34 . 2 grams sends the boiling-point up another half-degree to
101®. Continuing thus with five separate portions of 34.2
grams each, we should observe each time the same rise in the
boiling-point. It is really a little more than half of a degree
(0.52), so that the liquid after the introduction of the last
portion would boil at 102®. 6.

The condusiona are very definite and simple:

1. The rise in the boiling-point is proportional to the concen-
tration of the solution.

We have used, altogether, half of a molecular weight of sugar
(171 grams) and the boiling-point has risen 2®.6. Hence:

2. A molecular weight of sugar dissolved in 100 grams of water
causes a rise in the boiling-point of 5®.2.

Now conceive the same experiments repeated with glucose
(CeHi20e), the molecular weight of which is, in round numbers,
180. Each portion of 18 grams would raise the boiling-point of
100 grams of water about half a degree (0®.52) so that a whole
molecular weight would raise the hoiling-point 5®. 2.

In connection with this it will be interesting to invert (p. 195) »

* The change of sucrose into grape-sugar and f ruit-«ugar is called
inversion.

SUGAR SOLUTION 249

the cane sugar solution containing 171 grams of sugar in 100
grams of water and study the effect on the boiling-point. From
the equation:

C„H„ Oil + H,0 — ^ CeHi,0. + CeHi, O.
Cane Sugar Glucose Fruit sugar

it is clear that the inversion will double the number of molecules
of dissolved substance. It will also remove nine grams of water
(why nine?) which must be replaced before the boiling-point is
taken.

Practically, therefore, we add a trace of hydrochloric acid to
invert the sugar, nine c.c. of water to replace that used in the
inversion and then take the boiling-point. It is now 105**.2.
The inversion has doubled the rise. Half of a molecular weight of
glucose and half of a molecular weight of fruit sugar together
raise the boiling-point by the same amount as would a molec-
ular weight of cane sugar, 5° . 2. Plainly it is only the number of
molecules that counts. The kind, size or weight of the mole-
cules has no influence. We now have a basis for a third state-
ment:

3. A molecular weight of any non-electrolyte, dissolved in 100
grams of water, produces a rise in the boiling-point o/ 5**.2. Sub-
stances, like alcohol, which vaporize with the water, are ex-
cluded from this statement. Alcohol lowers the boiling-point of
water.

335. The Lowering of the Freezing-point — Sugar solution
freezes at a lower temperature than water. The attraction be-
tween the sugar molecules and those of the water makes it
more difficult for the latter to separate in the form of ice^ just
as it makes it more difficult for them to take the form of steam.
It is impossible to dissolve a molecular weight (342 grams) of
sugar in 100 grams of cold water but 34 .2 grams lower the freez-
ing-point by 1**.9 and the drop is proportional to the concen-
tration, so that 342 grams would lower it by 19®. Here, also,
the kind of molecule is without influence. 150 grams of glucose
would produce the same drop of 19**, and so would 46 grams of
alcohol (CjHeO = 46), for here there is no vaporization.

4. A molecular weight in grams of any non-electrolyte, dissolved in
100 grams of water produces a lowering of the freezing-point of 19®.

250 AN INDl/CTIVE CHEMISTRY

336. Liquids other than Water. — Solutions in other liquids
act in the same way. Thus, if the molecular weight of a sub-
stance can be dissolved in 100 grams of alcohol it will produce a
rise in the boiling-point of 11°. 5. Fractions of a molecular
weight produce a proportionate rise in the boiling-point. For
100 grams of acetic acid, the molecular rise of the boiling-point
is 25° and the molecular lowering of the freezing-point is 39°.

The most important use of these facts is in determining the
molecular weights of the countless new substances which are
constantly being prepared. Thus, suppose that 1 gram of a
substance, whose molecular weight was unknown, was found
to lower the freezing-point of 100 grams of acetic acid 0° . 5. We
know that the molecular weight, whatever it may 6c, would give a
lowering of 39°. Since the lowerings are proportional to the
quantities of substance dissolved, we have*

0°.5 : 39° : : 1 : Molecular weight

From which the molecular weight = 78.

337. Solutions of Electrolytes. — Let us now experiment on
the boiling-point of salt-solution. The molecular weight cor-
responding to the formula NaCl is 58.5. We dissolve one-
tenth of this (5.85 grams) in 100 grams of water, expecting a
rise in the boiling-point of about half of a degree. As a matter of
fact, the solution boils at about 101°. The rise is nearly double
what we should expect. A second portion of 5 . 85 grams sends
the boiling-point up to nearly 102°. Molecule for molecule, salt
has about twice as much effect on the boiling-point of water as
has sugar.

Before we attempt to explain this puzzling fact, let us try
some other electrolytes. Potassium chloride, so similar to
salt in most respects, shows the same behavior. The molecular
weight corresponding to KCl is 74 . 5 and 7 . 45 grams of it raise
the boiling point of 100 grams of water about twice as much as
the corresponding weight of sugar. Sodium hydroxide (NaOH
= 40) and potassium hydroxide (KOH = 56) act in the same
way. All four substances also lower the freezing-point of water
nearly twice as much as does the equivalent quantity of sugar.

338. Ions. — When the sugar was split by inversion into
glucose and fruit sugar the double number of molecules produced

SOLUTIONS OF ELECTROLYTES 261

a double rise in the boiling-point. This suggests an explanation
for the conduct of the salt solution. It seems that the rise in
the boiling-point depends only upon the number of molecules of
dissolved substance, and serves as a measure of this number.
A double rise means that the number is doubled. But the salt
molecule contains only two atoms, and the only way in which the
number of molecules can be doubled is by the separation of each
molecule into an atom of sodium and an atom of chlorine. Thus
the study of salt solution leads us straight to the conclusion that,
when salt is dissolved in watery its molecules break up into atoms
of sodium and atoms of chlorine j which move about in the liquid
independently of each other.

When the molecule of salt is broken up, the sodium atom takes
up a positive charge of electricity, while the chlorine atom is
i^egatively charged. These charged particles which are as-
sumed to be present in solutions of electrolytes are called ions,
a word due to Faraday y who laid the foundations of our know-
ledge of this subject. Their charges make them act very differ-
ently from ordinary atoms, as we shall see. The splitting of the
molecule into charged fragments, which occurs when electro-
lytes are dissolved in water, is called ionization.

How does the electric current pass through a salt solution?
The anode is simply a plate on which the dynamo or battery
keeps a permanent positive charge. Unlike charges attra,ct, so
the negatively charged chlorine ions are drawn to the anode,
where their charges are neutralized by its positive electricity.
They then unite in pairs to form molecules of ordinary chlorine
gas, which bubbles up from the anode.

In the same way, the negative charge on the cathode draws the
positive sodium ions to it. When their charges are neutralized
they are no longer ions. They are simply sodium atoms, which at
once interact with the water, producing hydrogen, which escapes
around the cathode, and sodium hydroxide, which dissolves.

The electrolysis of potassium chloride — which is carried out
on a large scale in Germany with the sylvite from Stassfurt —
is explained in the same way. We have only to substitute
potassium ions for the sodium ions.

With the chloride of a metal like copper, which does not in-
teract with water, matters are still simpler. The chlorine

252 AN INDUCTIVE CHEMISTRY

escapes at the anode, as before. At the cathode, the positive
copper ions give up their charges and separate as ordinary
copper, which forms a red plating on the cathode. Since the
ions of all metals are, like those of sodium, positively charged,
they always travel to the cathode. Hence, in electro plating,
the object to be plated is always connected with the cathode.

339. Questions often Asked, with their Answers. — 1. Ques-
tion: Why can the current not get through a sugar-solution?
Answer: In solutions, the current is carried only by the charged
bodies we have called ions. As the boiling-point showed, the
sugar dissolves as unbroken molecules. Therefore there are
no ions to carry the current.

2. Question: If a salt solution contains free atoms of chlorine,
why does it not smell of chlorine and bleach dye stuffs? An-
swer: The single charged atom which we call an ion of chlorine
is a very different thing from the pairs of uncharged atoms in
ordinary chlorine. There is no reason to expect it to act in the
same way.

3. Question: Why do not the free sodium atoms in salt so-
lution interact with the water, forming caustic soda and hydro-
gen? Answer: As in (2); the strong electric charge makes
the sodium ion quite different from ordinary sodium. When the
charge is given up at the cathode, the interaction does take place.

4. Question: How is it that salt is obtained unchanged when

salt solution is evaporated? Answer: Ionization is reversible.

Using Na, where + means a positive charge, as a symbol for
the sodium ion, and CI for the chlorine ion, we may write:

NaCl

This equation is to be read forward when the salt is dissolved,
and backward when it is separated by evaporation.

5. Question: Are all the salt molecules separated into ions, or
are there some unbroken molecules (NaCl) mixed with the ions
in the solution? Answer: In a concentrated salt solution there
are many unchanged molecules mixed with the ions. The more
the solution is diluted the more complete the ionization becomes.
When a molecular weight (58 . 5 grams) of salt is dissolved in a
liter of water, something like one-third of the total number of

I /

'/ •

SOLUTIONS OF ELECTROLYTES 253

^ molecules remains un-ionized. If the solution is diluted to 20

liters, the separation into ions becomes almost complete.

6. Qvsstion: Is it possible to separate the two kinds of ions,
and to obtain, for instance, a liquid containing only sodium ions
in one vessel and a liquid containing only chlorine ions in an-
other? Answer: No, the attraction of the positive and negative
charges prevents any separation of this sort. Thus, suppose
that in some way, we had succeeded in separating the sodium
and chlorine ions from only 58.5 milligrams (0.0585 gram) of
salt. A simple calculation shows that, even if the two vessels
containing the ions were a kilometer apart, the attractive force
between them would be equal to the weight of 8,500,000 kilo-
grams. The separation of such quantities of electricity would
produce disturbances which would make the most violent thun-
der storm a tame affair by comparison.

340. Ions of Bases and Acids. — A solution of sodium hy-
droxide is a good conductor, and the freezing- and boiling-points
are altered about twice as much as they would be by the equiva-
lent quantities of sugar. Therefore each molecule has split
into two ions. Just as in salt solution, the positive charge is
taken by the sodium atom. Then the negative charge must be
, taken by the rest of the molecule, which is the radical OH. The

r + —

^_ ^ ions in sodium hydroxide solution are therefore Na and OH.

In potassium* hydroxide solution they are K and OH. The
P peculiar and very similar properties of the two solutions are due

t \'i^ to the OH, which is called hydroxyl.

' ^ Hydroxyl is the characteristic ion of bases. It is present in

the solutions of all of them, and since it is the only constituent

which is common to them all, the bitter taste, the caustic action

on organic matter, the corrosive action on certain metals, the

effect on litmus and other dye stuffs and the interaction with

acids must be ascribed to its presence.

In a water solution of hydrochloric acid, the ions can only be
/ + — +

H and CI. The hydrogen ion, H, is quite a different thing from

hydrogen gas, H2. Thus, it is not combustible. It can only be ob-
tained in water solution, while H2, as we know, is scarcely soluble

+
in water. Hydrogen is tasteless, but H has an intensely sour taste.

254 AN INDUCTIVE CHEMISTRY

The ions of nitric acid are H and NOa. The hydrogen ion is
the characteristic ion of acids; it is the only constituent which is
common to water solutions of all of them and therefore the prop-
erties which they all have in common, the sour taste, the cor-
rosive action on most metals, the effect on litmus and other dyes
and the interaction with bases must be ascribed to its presence.

341. Comparison of the Hypothesis with the Facts. — Three
ways of testing this far-reaching conclusion suggest themselves:

1. A solution of hydrogen chloride in the hydrocarbon
toluene CtHb does not affect the color of litmus and has no action
on th« metals. Then it ought not to contain any hydrogen ions.
But if so, it cannot contain chlorine ions either; it must be a non-
conductor. Experiment shows that it does, in fact, obstruct the
passage of the current just as completely as a water solution
of sugar. Pure liquid hydrogen chloride, free from water, acts
in the same way: it is inactive toward litmus and the metals and
is a non-conductor.

2. Different acids act upon metals, like zinc, with very dif-
ferent speeds. For fair comparison the solutions of different
acids should be made to correspond in concentration. Active
acids like hydrochloric, liberate hydrogen rapidly in contact
with zinc. Inactive acids, like acetic, liberate hydrogen rmxh
more slowly^ under similar conditions. If we are right in ascrib-
ing the chemical activity of acids to the hydrogen ions this can
have only one meaning. There must be more hydrogen ions in
the solution of hydrochloric acid. A larger proportion of its
molecules must be separated into ions than in the acetic acid.

Then the solution of hydrochloric acid ought to be a better
conductor than that of acetic acid at equivalent concentration.
We have already seen that this prediction is verified. Active
acids, like hydrochloric, conduct well, inactive oHes, like acetic,
badlyy when dissolved in water.

3. The thermochemical equations for the neutralization of
hydrochloric and nitric acids in dilute solution, by caustic soda
and caustic potash are as follows:

(1) NaOH + HCl — >- NaCl + H2O + 13,700 Cal.

(2) KOH + HCl — >- KCl + H2O + 13,700 Cal.

(3) NaOH + HNOs — >■ NaNOs + H2O + 13,700 Cal.

(4) KOH + HNOa — >- KNOs + H2O + 13,700 Cal.

SOLUTIONS OF ELECTROLYTES 256

The fact that identical amounts of heat are produced
in all four cases is surprising. Even in changes so similar
as the syntheses of salt and of sylvite the heat values are
different:

(5) Na + CI >- NaCl + 98,000 Cal.

(6) K + CI — >- KCl + 106,000 Cal.

We must find some explanation for the fact that, while the
heat values of (5) and (6) are different, those of (1) and (2) are
identical. This would indicate that (1) and (2) are, in reality,
more nearly alike than a mere glance at the equations would
lead us to think.

Let us now apply the idea of ions to (1)

+ —

The NaOH becomes Na and OH.

+ —

The HCl becomes H and CI.

+ —

The NaCl becomes Na and CI.

The H2O remains H2O (being practically un-ionized)

The equation becomes:

+ — + — + —

Na + OH + H + CI — >- Na + CI + HjO.

+ —

BiU the Na and the CI have taken no part in the chemical change.

They are simply left over and can be subtracted from both sides

of the equation, which then becomes:

— +

OH + H — >- H2O.

Hydroxyl ions and hydrogen ions have combined to form water,

and that is all that has happened. If we evaporate the solution

+ —

the Na and CI will form NaCl, but that does not occur in dilute

solution.

Similar treatment of (2) gives:

+ + — + —

K + OH + H + CI — >- K + CI + HjO.

OH + H — >- H2O.

We can now state the reason for the identical heat values:
the two changes arCy at bottom^ the same.

256 AN INDUCTIVE CHEMISTRY

(3) and (4) can be handled in the same way:

(3) Na + OH + H + NOs — >- Na + NOa + H2O.

— +

OH + H — >- H2O.

+ — -f — + —

(4) K + OH + H + NO3 — >- K + NO3 + HsO

— +

OH + H — >- H2O.

342. General Statement. — Remembering that active, in this
connection, means completely ionized, we may put the whole
matter thus:

When an active base is neutralized, in dilute solution, by an
active acid the only change is the union of hydroxyl ions and
hydrogen ions to water. The heat valvs is, therefore, always
the same:

(7) OH + H — >- H2O + 13,700 Cal.

(7) Can be regarded as a general equation, which applies to
all cases of neutralization, where the base and the acid are al-
most completely ionized.

343. Normal Solutions. — From (7) it is plain that, in round
numbers, 1 gram of hydrogen ion interacts with 17 grams of hy-
droxyl ion. A water solution of an acid which is of such strength
that it contains 1 gram of hydrogen ion per liter is called a normal
solution. Such a solution would contain 36.5 grams of pure hydro-
chloric acid per liter, or 63 grams of pure nitric acid. The choice of
the acid is a matter of convenience. Oxalic acid may be used in
the laboratory studies. In that case the normal solution is made
by simply weighing out 63 grams of oxalic acid, the quantity
which will yield 1 gram of hydrogen ion. This is then dissolved,
and diluted to a liter in a flask with a graduation on the neck.

From (7) it appears that a liter of this liquid will neutralize
that quantity of any base which contains 17 grams of hydroxyl
ion, that is, 40 grams of sodium hydroxide, NaOH, or 56 grams
of potassium hydroxide, KOH. One cubic centimeter of it will
neutralize TiiW of these quantities, that is, 40 milligrams (0 . 040
grams) of sodium hydroxide, or 56 milligrams (0.056 gram) of
potassium hydroxide.

Normal solutions are constantly used by the working chemist.
Thus, suppose it is required to ascertain how much real sodium

SOLUTIONS OF ELECTROLYTES 257

hydroxide there is in a commercial sample of impure caustic
soda. One gram of the caustic soda is weighed and dissolved.
A few drops of litmus are added, which will turn the liquid blue.
Then the normal acid is added from a burette (Fig. 80) with con-
stant stirring. When all the sodium hydroxide is neutralized,
the liquid will turn red. Then the number of cubic centi-
meters of normal acid used are read off. Suppose, for illustra-
tion, that 22.5 c.c. of the normal acid were required.. Then
0.040 X 22.5, or 0.900 gram of sodium hydroxide must have
been neutralized. The caustic soda, therefore, contained only
90 per cent, of real sodium hydroxide, the remaining 10 per cent,
being water and other substances.

A normal solution of a base contains 17 grams of hydroxyl
ion per liter. Such a solution would contain 40 grams of so-
dium hydroxide in a liter. One cubic centimeter of it neutralizes
0.0365 gram of hydrochloric acid, 0.063 gram of nitric acid or
equivalent quantities of other acids.

The word alkali means a solution containing a base. The
sensitive dye stuffs, used in such experiments are called indica-
tors. Litmus is an example. There are many others. Cochi-
neal is orange with acids and violet in solutions containing bases.
Phenol-phthalein is colorless in acid solution and red when the
liquid contains a base.

Definitions

Electrolysis. Decomposition of a compound by the electric
current.

Base. A substance which tastes bitter, turns red litmus blue
and interacts with acids forming, with each acid, water and a salt.
A base is a hydroxidey usually of a metal, sometimes of a radical.

Electrolyte. A substance whose solution in water conducts the
electric current. Only acids, bases and salts are electrolytes.

Ions, Fragments bearing electric charges, into which the mole-
cules of electrolytes are separated in water solutions.

Ionization. The separation of the molecules into ions, which
takes place when acids, bases or salts are dissolved in water.

Indicator. A sensitive dye-stuff, like litmus, whose color is
strikingly changed by traces of acids or bases.

Alkali. A solution which conta^ins a base, and which, therefore,
reverses the color-changes in indicators produced by acids.

CHAPTER XXI

ELEMENTS WHICH RESEMBLE CHLORINE:
IODINE, BROMINE, FLUORINE

344. Halogens. — The four elements chlorine, iodine, bro-
mine ^d fluorine are called the halogen group. Tincture of
iodincy a deep brown liquid used as an application for
sprains, is familiar to the student. Like all of the druggist's
tinctures, it is a solution in alcohol. The dissolved sub-
stance is the element iodine, which was discovered by Cour-
tois, a Parisian saltpeter maker, in 1811.

345. Properties of Iodine. — Some facts cpnceming iodine
are sunmiarized in the following table:

Appearance: flat, black-gray crys- Sjrmbol: I.

tals with about the color and Atomic weight: 127.

luster of graphite. Melting-point: 114"*.

Boiling-point: 184"*. Color of vapor: deep purple.

Molecular weight: 22.4 liters of Formula: Is.

the vapor calculated to S.T.P.

weigh 254 grams.

Solubility: 100 c.c. water dissolves only 0.016 gram of iodine. It is
freely soluble in a water solution of potassium iodide (forming a
brown solution), in alcohol (tincture of iodine), in ether (brown
solution), in chloroform (purple) and in carbon disulphide (purple).

Chemical conduct: active, but less so than the other three members
of the group.

Valence: iodine, like the other halogens is univalent toward hydrogen
and the metals. Toward non-metals the valence is variable.

Uses: for making potassiimi iodide which is largely employed in
medicine, and iodoform (CHI3) which is a yellow powder used to dress
wounds in surgery; in the manufacture of complex carbon compounds
which are employed as dye stuffs.

World's annual production: about 500 tons, mostly from Chili, where
iodine compounds occur as an impurity in the great deposits of sodium
nitrate (Chap. XXIII).

346. Hydriodic Acid. — Hydrogen iodide, HI, resembles
hydrogen chloride. It is a colorless, suffocating gas, very

258

IODINE, BROMINE, FLUORINE 259

soluble in water and the solution is a good conductor and an

active acid. Hence the molecules must be largely separated

+ —

into H and I.

That iodine is less active than chlorine is plain when the behavior
of a mixture of equal volumes of hydrogen and iodine vapor is studied.
The union is sluggish and partial. At 450®, four-fifths of the two ele-
ments imite to hydrogen iodide; the rest remains in the free state no
matter how long the mixture is heated. That this is merely another
case of equilibrium dependent upon concentration, is proved when
hydrogen iodide alone is heated to 450®. The purple vapor of iodine
appears and one-fifth of the gas separates, producing a mixture of exact-
ly the same composition as that obtained by heating iodine vapor and
hydrogen to the same temperature.

Hydrogen iodide bums in oxygen, forming purple fumes of
iodine. Water is also formed:

2HI + — ^ H2O + I2,

The solution is slowly acted upon in the same way by the
oxygen of the air and turns brown from the iodine liberated.
Related to this behavior is the fact that hydrogen iodide
cannot be made by the action of sulphuric acid upon an
iodide, like potassium iodide. The oxygen of the sulphuric
acid oxidizes the hydrogen iodide, so that iodine is the chief
product, very little hydrogen iodide being obtained. The
water solution of hydrogen iodide is called hydriodic acid.
It can be made by passing hydrogen sulphide into water in
which powdered iodine is suspended:

H2S + I2 — ^ 2HI + S.

The sulphur is removed by filtration. Hydriodic acid is
employed in medicine.

347. Potassium Iodide. — Potassitim iodide, KI, which is
largely used in medicine, is the most important iodine com-
pound. It forms colorless cubes, which slowly turn yellow
in the air from separated iodine. Its specific gravity is 3.
It melts at 700°, and 100 c. c. water dissolves, at 18°, 138
grams of it. It is also soluble in alcohol.

260 AN INDUCTIVE CHEMISTRY

348. Tests for Iodine. — ^When chlorine is passed into a
solution of potassium iodide, the coloriess liquid turns brown
and a gray-black powder of iodine separates. Solutions of
other iodides act in* the same way, for the metal ions play no
part. The chlorine takes the negative charges from the
iodine ions, converting them into ordinary iodine:

21 + CI2 —>- 2Ci + I,.

Iodine can be obtained from seaweed by treating a water
solution of the ashes with chlorine.

Sometimes traces of iodine, insufficient to color the water must be
tested for. In such cases, after passing in a little chlorine, chloroform
is added and the mixture shaken. The chloroform dissolves the iodine
and forms a purple layer at the bottom of the mixture. This makes the
test more dehcate, because almost all the iodine can be collected in a
few drops of chloroform.

Or, the starch test, which is wonderfully delicate, can be used.
Iodine ions (solutions of iodides) do not affect starch, but iodine mole-
cules (free iodine) dye starch intensely blue. A little starch paste made
by boiling starch with water, is mixed with the solution suspected of
containing iodine ions. If the latter are really present, a little chlorine
will now produce a deep blue color which serves to identify the merest
traces of iodine. We have seen (p. 191) that iodine solution can be
used as a test for starch.

349. Bromine: Discovery. — In the extraction of salt from
sea water (p. 206), the liquid is evaporated to about one-
twentieth of its original volume. The liquid which remains
when the salt has separated is called the mother liquor of
the salt crystals. Those substances which are present only
in traces in sea water remain dissolved, when the salt sepa-
rates, and the mother hquor contains them, in twenty-fold
the original concentration.

In 1826 J, A, Balard made some experiments with the
mother liquor of the salt basins at Montt)ellier, in southern
France near the Mediterranean. He found that chlorine
gas produced a red color in the liquid. He then distilled
and obtained a dense red liquid which proved to be a new
element. It had such an offensive odor that it was named

IODINE, BROMINE, FLUORINE 261

bromine from the Greek word for stench. Sea water contains
bromine ions, and in Balard^s experiments, the chemical
change was similar to the action of chlorine upon a solution
of an iodide. The chlorine took the negative charge from the
bromine ions:

2Br + CI2 —>- 2C1 + Br2.

350. Preparation. — The mother liquor of the Stassfurt salt
deposits contains bromine ions. So does the mother Uquor
from salt wells in Ohio, Michigan and Kentucky. These two
sources divide the world's production about equally.

In one method of extraction, the liquid is allowed to drip
through a sandstone tower packed with cylinders of fire
brick. Chlorine gas, obtained from a cylinder of liquid
chlorine, is passed in at the bottom. The liquid containing
the dissolved bromine flows into a vessel made of granite
slabs, where it is heated by steam, to separate the bromine by
distillation. The bromine is condensed in another vessel.

351. Properties of Bromine. — The following table gives
some information about bromine:

Symbol: Br. Specific Gravity: 3.

Formula: Br2. Melting-point: -7".

Atomic weight: 80, Boiling-point: ed*".

Appearance: Dark red liquid.

Solubility: 100 c.c. water at 18** dissolves 3 grams; it is more soluble in
ether, carbon disulphide and chloroform, which therefore extract it
from water as they do iodine, but less completely. All these solutions
are red.

Bromine has a severe caustic action on the skin, which it
stains yellow. It gives a yellow color with starch paste, but
the test is not delicate. Its vapor is red and escapes freely
from the liquid even in the cold. The vapor has an un-
bearable smell, and sharply irritates the eyes, nose and
throat.

Bromine is an active element, more so than iodine, but it
is less active than chlorine. It forms bromides upon con-
tact with the metals. In many cases the combination is
18

262 AN INDUCTIVE CHEMISTRY

violent. Tin bums brightly when dropped into bromine,
and potassium explodes. In most respects bromine stands
between chlorine and iodine, but the fact that no oxide of
bromine exists is a point in which it resembles fluorine (see
below).

Bromine finds its chief uses in the manufacture of potassium
bromide and of complex carbon compounds which are to
serve as dye-stuffs, drugs or perfumes. It is a good bleach-
ing agent and an excellent*disinfectant, but is never employed
for these purposes. (Why not?)

352. Hydrobromic Acid. — Hydrogen bromidef HBr, close-
ly resembles hydrogen chloride. It is a colorless, suffocating
gas. 100 c.c. water dissolves 60 Uters of it at 10**. The
solution is an active acid.

353. Potassium Bromide and Sodium Bromide. — Potas-
sium bromide, KBr, is the most important bromine compound.
It forms white cubes, freely soluble in water. It is much
employed in photography.

Sodium bromide, NaBr, resembles potassium bromide.
Both are extensively used in medicine, for disorders of the
nervous system.

354. Fluorine: Fluor spar. — The common mineral fluor
spar is found in transparent cubes, which are often violet,
yellow or green. It frequently occurs with ores of the metals,
especially of lead. The crystals are soft enough to be
scratched with a knife point, and this serves to distinguish
fluor spar from other minerals which resemble it, but are
harder.

355. Chemical Nature of Fluor spar. — When a bit of fluor
spar is held in the Bunsen flame, it melts easily (hence the
name from the Latin Jluere, to flow) and colors the flame
bright orange. The color will be familiar to the student, for
the light of the flaming arc lamps, which have become so com-
mon, has the same shade. The ''carbons'* of these lamps are
made of a mixture of carbon with fluor spar and other sub-
stances.

IODINE, BROMINE, FLUORINE 263

This orange flame-color is a test for the element calcium,
a grayish white metal, which resembles sodium, but is harder
and less active. We shall study it in Chap. XXIV.

Calcium, then, is the metallic constituent of fluor spar.
The non-metallic constituent cannot be obtained by direct
decomposition of the mineral, for the elements of fluor spar
are so firmly imited that direct separation is impossible.

356. Hydrofluoric Acid. — The behavior of fluor spar with
sulphuric acid indicates clearly that it is similar in chemical
nature to table-salt, that is, that the calcium is combined
with an element which resembles chlorine. A little of the
powdered mineral can be heated gently with strong sul-
phuric acid in a lead dish. The colorless, poisonous gas
which escapes smells like hydrogen chloride, produces a white
cloud with a glass rod wet with ammonia, and reddens blue
litmus paper. It is hydrogen fluoride, HF, the hydrogen
compoimd of fluorine, which is the non-metallic element of
fluor spar.

If the dish containing the fluor spar and sulphuric acid is
covered with a glass plate, the lower surface becomes white
and opaque. Glass is rapidly attacked by hydrogen fluoride,
and use has been made of this fact for more than two cen-
turies, in the etching of glass. Either hydrogen fluoride, or
its solution in. water can be used for this purpose. The glass
is covered with wax, which is not attacked by the acid, and
the pattern is cut through the wax with a sharp instnunent
which lays bare the glass. Exposure to hydrogen fluoride
will then etch the pattern permanently upon the object.

To obtain a water solution of hydrogen fluoride, the mix-
ture of fluor spar and sulphuric acid can be heated in a lead
retort, and the gas passed into water contained in a lead vessel.

The solution is a colorless, acid liquid, similar to hydro-
chloric acid. It is called hydrofluoric add. It dissolve??
many metals, forming fluorides, with escape of hydrogen:

Zn + 2HF —>- ZnF2 + Hj.

264 AN INDUCTIVE CHEMISTRY

These interactions are not as rapid as those of hydro-
chloric acid under the same conditions, for hydrofluoric
is a much less active acid and the solution contains little
+ _

H and F and much un-ionized HF. For this reason, the solu-
tion b a poor conductor.

Great care must be taken not to get hydrofiuoric acid on the
skin, upon which it produces dangerous VMmnds. It is kept
in bottles of hard parafBne, on which it haa no action.

357. Fluorine. — It is a difficult and dangerous matter to
make hydrogen fluoride free from water. Anhydrous hydro-
gen fluoride is a colorless liquid, which must be kept in a
freezing mixture, for it boils at 19°. It is a non-conductor,
but when it contains dissolved potassium hydrogen fluoride

+ '_
(KHFi) the K and F ions carry the electric current through
the liquid. At the cathode, the potassium interacts with the
hydrogen fluoride,
liberatmg hydrogen;
iL attheanode,/wonn«,
the non-metallic ele-
ment of fluor spar,

Fig. 82 is a diagram of
the apparatus used by
Moissan, who i8o1at«d
fluorine in 1836, over-
Fio. S2.— The isalatian oC auorioe. coming the difficulties

which had balBcd
chemists tor a century. The U-ahaped tube contained 100 c.e. of the
solution of potassium Hydrogen fluoride in anhydrous hydrogen fluoride.
For his flrst eiqierimente, the apparatus was made of platinum ; later he
found that copper, which is only slightly attacked by fluorine, could be
used. The electrodes are of platinum and the stoppers, through which
they pass, of fluor spar, which is unaffected by fluorine. (Why?) The
U-tube is immersed in liquid methyl chloride, which is made to evapor-
ate rapidly by a current of air. This keeps the temperature down to
-50°; otherwise the hydrogen fluoride would boil away, owing to the
heat produced by the passage of the electric current.

IODINE, BROMINE, FLUORINE 265

The hydrogen is simply allowed to escape from the side tube in the
cathode limb. None of it must be allowed to get over into the anode
limb, for violent explosions would result. The fluorine is led through a
platinum coil cooled to -50° to condense any hydrogen fluoride which it
contains, and then through platinum bulbs containing sodium fluoride,
NaF, which absorbs the last traces of hydrogen fluoride. It then
passes into the platiniun or fluor spar tube containing the substance
whose interaction with it is to be studied. In many cases, glass test
tubes can be used, for pure fluorine has little or no action on glass.

358. Properties of Fluorine. — Some information concern-
ing fluorine is summarized in the following table:

Symbol: F. Boiling-point: — 187**.

Formula: F2. Freezing-point:— 223°.

Atomic weight: 19.

Color: Similar to that of chlorine, but paler.

Odor: Similar to that of chlorine.

Action on the Body: Irritates eyes and respiratory passages.

Chemical conduct: Most active of the elements. Combines directly

with most other elements, and the combination is attended, in

many cases, with combustion.
Liquid fluorine is yellow and has about the same specific gravity as
water.

Fluorine acts violently upon most compounds. When it is passed
into a test tube containing a little table salt, chlorine gas and sodium
fluoride are produced:

NaCl + F — >- NaF + CI.

Other chlorides behave in the same way. In the case of bromides, the
bromine which is liberated at first, bums in the fluorine to a fluoride of
bromine. Iodides behave like bromides.

As a rule, chemical changes become so slow at very low temperatures
that practically they may be said not to occur at all. Substances which
interact vigorously at room temperature may be left in contact at
-200° without any apparent effect. It is noteworthy, therefore, that
liquid fluorine still takes part in violent chemical changes when cooled
by boiling liquid air (-190°). This is a striking instance of the chemical
activity of fluorine. When liquid fluorine is spilled on a wooden floor,
a flame appears which is due to the combination of the fluorine with the
hydrogen of the wood.

359* Occurrence. — Like the other members of the chlorine
group, fluorine scarcely occurs in the free state. Its com-

266 AN INDUCTIVE CHEMISTRY

pounds are much more abundant than those of bromine or
iodine. Traces of fluorine compounds are contained in river
and sea-water, in the bones (especially the enamel of the
teeth) and in many plants.

The chief mineral containing fluorine is fluor spar (see
above) which is calcium fiuoridef CaF2. Fluor spar serves
as the raw material for the manufacture of hydrofluoric
acid, and is also used in the making of opal glass. Fluor spar
is added to the melted glass. On cooling it separates in
countless little crystals which render the glass cloudy.

Another important compound is cryolite, NasAlFe, which is
a white mineral with a greasy luster, found in Greenland.
It has been referred to in connection with the manufacture
of aluminium (p. 129). It is used in making alum (Chap.
XXII). Cryolite is much used, in the same way as fluor
spar, in the preparation of opal glass.

Related Topics

360. The Halogens as a Group of Elements. — We have seen
that the members of the chlorine group unite with the metals,
producing compounds more or less like table-salt. Hence they
are called the halogens, which is from the Greek, and means saUr
formers.

The fact that the activity of the halogens increases with de-
creasing atomic weight from iodine (I = 127) to fluorine (F =
19) has been pointed out. This is especially clear (1) from their
combination with hydrogen to form the acids of the formula
HI, HCl, HBr and HF, and (2) from the interaction of some of the
halogens with water, forming the same acids, with escape of oxygen,
for instance:

H,0 + 01, — >- 2 HCl + O.

The heat values in (3) , in the following table, refer to the
simple equations like

H + 01 — >- HOI

in which single atomic weights unite. The iodine and bromine
are supposed to be used in the form of vapor. The increase in
the chemical energy with decreasing atomic weight is strikingly

IODINE, BROMINE, FLUORINE

267

shown in the heat value, which is about 100 times as great for
fluorine as for iodine, although the actual weight of fluorine
used is only about one-seventh of that of the iodine.

(1)
Element

Iodine

Bromine

(2)
Behavior with Hydrogen

(3)

Heat Value
of (2)

Chlorine

Fluorine

Slow, partial combina-
tion when heated.

Complete combination
when heated. No ex-
plosion with flame or
in sunlight.

No action in dark. Ex-
plodes in simlight or
when flame is applied.

Explodes at once even in
the dark and without
flame being appUed.

400 Cal
12000 Cal

(4)
Behavior with Water

26000 Cal

39000 Cal

No mteraction.

Slow escape of oxygen
in simlight.

Oxygen escapes in sim-
light more rapidly than
in the case of bromine.

Explosive liberation of
oxygen [as ozone (^)]
even in the dark.

361. Photography.— Silver chloride darkens when exposed
to light. Chlorine escapes and the dark substance formed is at
first silver sub-chloride AgaCl:

2AgCl — >- AgaGl + Gl.

Later, if the exposure to light continues, the sub-chloride loses
its chlorine, leaving silver:

AgaCl — >- 2 Ag + CI.

Talbot, in 1839, showed how this fact could be used for pic-
ture-making. If a paper is dipped in a solution of table salt
and then in one of silver nitrate Ag NOs, silver chloride is formed
in the paper*

AgNO, + NaCl — >- AgCl + NaNOs, or Ag + CI — >- AgCl.

The paper must then be kept in the dark, for it is sensitive
to light. If a semi-transparent object, like the wing of a butter-

* Ozone is a form of oxygen which will be studied in Chap, XXIV.

268 AN INDUCTIVE CHEMISTRY

fly, is pressed out against a glass plate, with a piece of sensitive
paper back of it, and exposed to light, a copy will be obtained,
but it will be dark where the wing is light and light where the
wing is dark. Where there is a dark spot, little light will get
through the wing, and a white area on the paper will result,
but a clear area allows much light to pass and strongly blackens
the paper beneath.

Another difficulty in making pictures in this way is that they
can only be examined by candlelight. On account of the unchanged
silver chloride in them, the white portions are still sensitive to hght,
and, if exposed, the whole picture soon turns black. Photogra-
phers' "proofs" act in the same way, for the same reason.

Talbot overcame this difficulty by soaking the picture in a
strong solution of table-salt. This dissolves the silver chloride
out of the paper, and, of course, the sensitiveness to light goes
with it. The astronomer Herschel afterward found that a solution
of *'hypo" was better than salt solution. "H3rpo" is sodium thio-
sulphate, Na28208. Its solution rapidly dissolves silver chloride
and silver bromide.

362. Silver Bromide. — Silver bromide is a yellow-white sub-
stance, "insoluble" in water (100 c.c. water dissolves 0.00001
gram). It forms when silver ions and bromide ions come to-
gether, for instance:

AgNOi + KBr — ► AgBr + KNO,.

or, since any soluble silver salt and any soluble bromide will

answer:

+ -
Ag + Br — >«• AgBr.

Exposure to light for even a small fraction of a second has a
remarkable effect upon silver bromide. The appearance of the
salt is unchanged, but it is much more easily converted into silver
than before. Modern photography is based upon this fact.

There are complex carbon compounds, like pyrogallol, which
are called, by the photographer, developers. Upon silver
bromide which was made in the dark, and has never been ex-
posed to light, pyrogallol solution has only a very slow action ;
but silver bromide, which has been acted upon by light for even
a hundredth of a second, is rapidly converted into metal by it.

IODINE, BROMINE, FLUORINE 269

A photographic plate is a glass rectangle, one surface of which
is covered with a film of hardened gelatin containing silver
bromide. In the manufacture, the gelatin is dissolved in
warm water and ammonium bromide and silver nitrate added:

AgNO, + NH^Br — >- AgBr + NH4NO,.

Ammonium
nitrate

The liquid is kept warm for a time, during which the fine
amorphous silver bromide which is first formed collects into
larger crystalline grains. This is called **ripening" and greatly
increases the sensitiveness of the plates. Then the mass is
allowed to cool to a jelly which is cut up, and the ammonium ni-
trate removed by washing with water.

After drying and remelting, the "emulsion," as it is called, is
poured upon glass plates, which, when dry, are ready to be
packed in light-proof boxes. The whole manufacture is con-
ducted in a dim red light, too weak to affect the emulsion.
Films are made in the same way, except that the backing is
transparent celluloid, instead of glass.

In taking a picture, the plate is placed in the camera, in such a
way that the sensitive surface is in the focus of the lens. After the
exposure to light, the plate looks just the same as before. But
when it is developed, a black deposit of silver is produced wherever
the light has acted.

The next step is to dissolve and remove the imaltered silver
bromide, to prevent it from being acted on by light, which would
turn the whole plate black. This is called "fixing" and is accom-
plished by soaking the plate in a solution of sodium thiosulphate
("hypo").

The thoroughly washed and dried plate is now called a nega-
tive. One reason for this name is that the lights and shadows
of the original are reversed in it. The light portions in the
original are represented by blackish silver, while the dark areas
in the original are clear glass in the negative. Another reason
for the name is that the arrangement from right to left is re-
versed in the negative, which, in this respect, is like a mirror-
image.

In printingf the negative is exposed to light with a piece of
sensitive paper back of it, in contact with the image. The light

270 AN INDUCTIVE CHEMISTRY

passes easily through the clear portions, which therefore become
dark in the print, but is arrested by those parts which are covered
with opaque silver, which remain white on the paper. Hence
the lights and shadows are again reversed and, with care, can be
made the same in the print as in the original.

Various papers are employed for printing. A very common
kind is covered with a film of starch or egg-albumin containing
silver chloride. When such paper is exposed to sun-light, silver
is rapidly produced, so that the progress of the printing can be
followed by inspection, but the picture has an unpleasant red-
dish color. If the print is afterward dipped into a solution con-
taining gold chloride, part of the silver of the image is replaced
by gold, which darkens it to a more satisfactory tint. This proc-
ess is called toning.

The "developing" papers, like "Velox," work on the same
principle as a plate. The sensitive layer is a film of gelatin
containing silver bromide or chloride, and, when briefly exposed
back of a negative, the paper remains white, but the picture
appears upon dipping it into the developer. The light of a
Welsbach mantle or an incandescent lamp can be used. The
print needs no toning.

Both these kinds of paper require "fixing" after the picture
appears. The unaltered silver chloride or silver bromide, as the
case may be, must be removed, otherwise the whole print would
shortly turn black. This is accomplished in the same way as
with a plate, by soaking in a solution of sodium thiosulphate, and
washing.

In platinotypes, the picture consists of finely divided plati-
num, and in some carbon prints, of lampblack. Both have the merit
of absolute permanence, since both platinum and carbon are
unaffected by the air.

Definitions

Flaming arc lamp. A lamp in which most of the light is radiated,
not from the carbons, but from a mass of incandescent vapor
between them.

Halogen, One of the four members of the chlorine group of
elements.

Developer, A substance whose behavior toward silver bromide
depends upon whether the silver bromide has been exposed to light

IODINE, BROMINE, FLUORINE 271

or not. If the silver bromide has been exposed to light, a developer
rapidly converts it into silver; if not, the developer does not affect it.

Emvlsion, A solution of gelatin containing suspended silver
bromide, ready for use in the manufacture of photographic plates
or films.

Fixing, Soaking an exposed and developed plate in a solution
of "h3T>o" to remove the unchanged silver bromide.

Negative. The product obtained by exposing, developing and
fixing a photographic plate.

Toning. Altering the color of a photographic print by a chemical
process.

BOOK V

ACIDS CONTAINING OXYGEN, AND THEIR SALTS

INTRODUCTION

Here we leave the compounds containing only two ele-
ments, which have, with some necessary exceptions, furnished
the main subject matter of the first four books, in order to
devote ourselves to the study of some important compounds
containing three elements.

The most important of these compounds, which fall within
the scope of an elementary treatment of our science, are the
acids containing oxygen, and the salts of these acids. Sul-
phuric acid, nitric acid, carbonic acid, boric acid, phosphoric
acid, silicic acid and their salts are the subjects to which
we shall now give our attention. Many of these compounds
have not only scientific, but also practical interest. Some of
them form the foundation of great mdustries.

We shall then discuss, very briefiy, some important com-
pounds containing the four elements carbon, hydrogen,
oxygen and nitrogen. The concluding chapters will be
devoted to the classification of the elements and to the sub-
ject of chemical calculations.

273

CHAPTER XXII

SULPHUBIC ACID AND ITS SALTS— HYDROLYSIS— THE
ELECTROLYSIS OF DILUTE SULPHURIC ACID

363. Beha^or of Sulphur Trioxide with Water.— When the
silky white needles of sulphur trioxide SOj (p. 97) are
dropped into water, explosive interaction occurs and much
heat is evolved. When-the liquid cools, it is found to redden
blue litmus, to act upon metab liberating hydrogen,

and to conduct the electric
current. It contains, there-
fore, an active acid to which
the name sulphuric acid
has been ^ven.

Direct combination of the
sulphur trioxide and water
must have occurred, for no
gas escapes and the liquid
contains nothing but a solu-
tion of sulphuric acid. The
simplest interpretation of
these facts is the equation:

Fio. 83.— Preparation of lulphurio ftdd SOj + HjO >- HjSO,.

by the uootact prooen . ■ . , ■ i . . i

Analysis of sulphunc acid
and its salts, which are called the sidphales, shows that
HiS04 is, in fact, the correct formula of the acid, and that
the sulphates are formed by the replacement of one or both
atoms of hydrogen by metals.

364. "Contact Process" for Sulphuric Add. — Sulphuric acid is
largely made from sulphur trioxide and water, the sulphur trioxide
being obtained by the method described on p. 96. The first step in
the process is to bum pyrite, FeSj, in tumaceH, with more air than is
necessary, so that the gases produced contain an excess of oxygen
aloDg with the sulphur dioxide. After being cooled and carefully puri-

274

SULPHURIC ACID AND ITS SALTS 275

fied, the gases enter at A, the bottom of the "contact apparatus"
(Fig. 83), which is an upright cylinder containing four tubes, fitted with
perforated shelves. Upon each shelf is a layer of asbestos, coated with
platinum powder. The gases pass upward around the outside of the
tubes, and enter them at the top. The object of this arrangement is
to cool the tubes. This is necessary, because the chemical change
which takes place in them evolves much heat:

SO2 + O — >- SOs + 23,000 Cal.

Another advantage is that the gases are warmed to the proper tempera-
ture (400**) before they enter the tubes.

Laden with fumes of sulphur trioxide, the gas passes into the bottom
of the absorption towers down which strong sulphuric acid trickles. This
rapidly and perfectly absorbs the sulphur trioxide, which dissolves in
the acid. By cautiously diluting this solution with water, sulphuric
acid of any desired strength can be made.

365. Tests for Sulphuric Acid. — ^A solution of barium chloride BaCl2
is added to some dilute sulphuric acid. A white precipitate of barium
sulphate BaS04 is formed:

BaCl2 + H2SO4 — >- BoSOi + 2 HCl.

However, a solution of any sulphate will give the same precipitate

when barium chloride is added. The test is for the SO4 ion. Hence we

may write:

++
SO4 + Ba >- BaS04.

Sulphuric acid can be distinguished from a sulphate by adding a
pinch of sugar and evaporating almost to dryness. Sulphates have no
effect, but sulphuric acid blackens the sugar, producing impure charcoal.

366. The Lead Chamber Process for Sulphuric Acid. — Some water,
which has been warmed imtil it gives off vapor freely, is poured into a
liter flask. A Uttle powdered sulphur is heated in an iron spoon until it
begins to bum and is then held in the flask until the air in the latter is
charged with sulphur dioxide, when it is withdrawn.

The mixture of gases in the flask now contains sulphur dioxide, SO2,
water, H2O, and oxygen from the air. These substances might interact
to form sulphuric acid, thus:

SO2 + HO2 + O ^ H2SO4.

That this really occurs can be shown by corking the flask and, after
a day or two, testing the Uquid with barium chloride. But the precipi-
tate of barium sulphate is scanty, and it is plain that the production of
sulphuric acid is too slow for practical purposes. We need a catalyzer
which will accelerate the^process.

276

AN INDUCTIVE CHEMISTRY

Instead of corking the flask, let us hold in it a glass rod wet with
nitric acid. A red gas, which is familiar to the student from his labora-
tory work, surrounds the rod. It is nitrogen peroxide, NO2, and is a
frequent product of chemical changes in which nitric acid takes part.
The barium chloride test applied to some of the liquid in the flask now
shows that a large quantity of sulphuric acid has been produced. An-
other portion, evaporated with a little sugar, leaves a black mass of
charcoal. Conclusions:

1. Sulphur dioxide, water vapor and oxygen interact very slowly to
form sulphuric acid.

2. Nitrogen peroxide is a catalyzer which enormously accelerates the
change.

The way in which these facts are apphed in the lead chximher process
will be imderstood from a study of Fig. 84. The sulphur dioxide is made

Lewi Ghambera

^ To .
Cbtmney

FiQ. 84a. — Preparation of sulphuric acid by the lead chamber process.

by burning pyrite, and more air than is necessary for the combustion is
admitted, so that the gases leaving the furnaces still contain about 10%
by volume of oxygen. They then enter the bottom of the "Glover tower,"
(Fig. 846), which is a tower 30 ft. or more high, made of lead lined
with fire brick, and packed full of little fire brick cylinders, open at both
ends. Here the gases are charged with nitrogen peroxide, in a way
which will be explained presently.

They then enter the first lead chamber, where the deposition of sul-
phuric acid begins; the others simply continue the interaction and push
it to completion. These chambers are made of thin sheet lead sup-
ported by wooden scaffolding. They are placed upon pillars, so that
the bottom is accessible for repairs. A single chamber may be as much
as 100 ft. long, 40 ft. wide and 40 ft. high. The water (more than the
equation requires) is introduced into the chambers in a fine spray, or
as steam. Short, wide lead tubes carry the gases from one chamber to
the next.

SULPHURIC ACID AND ITS SALTS 277

The sulphuric acid fallg, ae a fine rain, to the bottom of the chambere.
The escess of water dilutes it, so that the solution contains ooly about
60% of sulphuric acid. From time to time the acid is run off through
tubes into a lead reservoir.

Since the action of the nitrogen peroxide is catalytic, it is not used up
in the lead chambers, and since it is expensive it muet be saved from the
waste gases and used again.
This is the important func-
tion of the "Gay-LuBsac
tower" (Fig. 84c), up
through which the gases
pass before they are allowed
to escape. It is of lead, 30
to 60 ft. high, and is packed
with coke, over which
trickles concentrated sul-
phuric acid. This absorbs
the nitrogen peroxide, so
that the waste gases are
almost free from it.

We can now understand
how the gases from the f ur-
nacea are charged with nitro- p,^ ^^ p,^ B^_

gen peroxide in the Glover

tower, before they enter tiie lead chambers. The concentrated sulphuric
acid containing nitrogen peroxide — which is called "nitrose" — is pumped
from the bottom of the Gay-Lussac tower to the top of the Glover
and is allowed to trickle down over the little cylinders of fire brick.
Through another tube, acid from the lead chambers, containing 40%
of water, is run into the top of the Glover, where it mixes with
the nitrose.

Nitrogen peroxide will not remain absorbed in sulphuric acid if water
is added. When the acid is diluted enough to bring the percentageof
H2S04down to about 70% by weight, the nitrogen peroxide bubblesout
of the liquid as a gas. The 40% of water in the chamber-acid dilutes
the nitrose so far that the nitrogen peroxide escapes from it and is
swept into the first lead chamber. This escape takes place all the more
readily, because the gases in the Glover are fresh from the furnaces and
are hot (300°) . Small quantities of nitric acid are run in at the top of
the Glover from time to time to make up for the unavoidable losses of
nitri^en peroxide.

He sulphuric acid which comes out at the bottom of the Glover is
quite concentrated (over 80%), for much water has been boiled out of
19

278 AN INDUCTIVE CHEMISTRY

it in dripping over the hot cylinders of fire brick. It is ready to be
pumped to the top of the Gay-Lussac tower for use in absorbing the
nitrogen peroxide out of the waste gases.

Right here, then, is the foundation of the lead chamber process. From
the Glover to the Gay-Lussac the nitrogen peroxide passes, through the
lead chambers, doing its work of accelerating the production of sulphuric
acid. In the Gay-Lussac it is dissolved in strong sulphuric acid and then
pumped back to the top of the Glover where the round begins again.

The chemistry of the lead chamber process has been the subject of
much discussion. We have seen that two facts are beyond question: —

1. Sulphuric acid is formed very slowly from sulphiu* dioxide, water
and oxygen: —

SO2 + HsO + O — ^ H2SO4.

2. The formation of sulphuric acid, according to the equation just
given, becomes rapid if, in addition to the sulphur dioxide, water and
oxygen, nitrogen peroxide, is also present.

The only question is as to how the nitrogen peroxide acts in acceler-
ating the interaction. The simplest and most probable explanation
is that sulphur dioxide, water and oxygen, interact with the nitrogen
peroxide to produce sulphiuic acid and nitric oxide: —

SOj-f HjO+O+NOj — >- H2SO4+NO. (1)

nitric
oxide

We shall see, in the next chapter, that nitric oxide instantly unites
with oxygen, forming nitrogen peroxide: —

NO+0 >- NO2, (2)

The nitrogen peroxide formed in this way at once interacts with a
new portion of sulphur dioxide, water and oxygen, and forms an addi-
tional quantity of sulphuric acid, according to equation (1). According
to this explanation, a trace of nitrogen peroxide could produce an unlimi-
ted quantity of sulphuric acid. In actual work, there are losses of
nitrogen peroxide, which are compensated by adding nitric acid at the
top of the Glover tower. Nitric acid forms nitrogen peroxide, when in
contact with sulphur dioxide: —

SO2+2HNO3 >- H2SO4+2NO2,

so that adding nitric acid to the Glover amounts to the same thing as
injecting fresh nitrogen peroxide into the lead chambers.

367. Properties of Sulphtiric Acid. — Following are some
of the properties of sulphuric acid:

Appearance: colorless oil. Specific gravity: 1.854.

BoiUng-point : SSS^'C. Familiar name: "oil of vitriol."

SULPHURIC ACID AND ITS SALTS

279

Chemical properties: active acid, but less so than hydrochloric or

nitric acid.
Action on plant and animal matter: blackens and destroys it; energetic

caustic action on skin and clothing.

Sulphuric acid produces much heat when it comes into
contact with water. This is partly due to the formation of
the ions:

H2SO4 Z^ 2H + SO4.
+
The dilute acid (ions H and SO4) and the concentrated acid

(un-ionized molecules H2SO4) behave very differently, for
instance:

Inter-
action

Zinc

Iran

Copper

Dilute (ions)

Rapid escape of hydrogen

+ ++

Zn + 2 H >• Zn +H2,

zinc sulphate is obtained

when the liquid is evaporated.

Similar to zinc:
++ ++

Fe + 2H >- Fe + H2

Iron sulphate can be obtained

from the Uquid.

No action.

Concentrated (molecules)

Noactionin the cold. When
heated, hydrogen sulphide
escapes, water and zinc
sulphate being produced.

Hardly affects iron. Is often
transported in iron tank-
cars.

When heated, sulphur di-
oxide escapes, while cop-
per sulphate and water
are also produced.

368. Uses. — The world's annual production of sulphuric
acid is about five million tons, mostly made by the lead
chamber process, which yields an acid containing about 40%
of water. This 60% acid is cheap and is used whenever the
presence of the water is not objectionable. Thus, in the
manufacture of fertilizer from phosphate rocky the powdered
rock is treated with sulphuric acid. This one use takes about
half the total production of sulphuric acid. Great quantities of
chamber-acid are also used in making suZp/ia<cs, especially a??!-
monium sulphate, sodium sulphate and aluminium sulphate.

280 AN INDUCTIVE CHEMISTRY

The industries which need an acid nearly free from water
are supplied by the contact-process. Such acid is required
in the refining of petroleum (p. 188), in the manufacture of
explosives Uke nitroglycerin and gun cotton, and in the prep-
aration of dye-stjuflfs. Sulphuric acid free from water can
also be made from the chamber-acid, if conditions make it
profitable to do so. All that is necessary is to heat the cham-
ber-acid gently, until the water is evaporated. Since the
boiling-point of sulphuric acid is very much higher than
that of water, practically no acid escapes with the water
vapor. Dishes made of fused quartz are employed to contain
the chamber-acid. They are heated by the waste heat of
the pyrite furnaces.

369. The Sulphates: Copper Sulphate. — "Blue vitriol"
was known to the alchemists and named by them from
its glassy blue crystab* For the same reason, it is often
called "bluestone." The specific gravity of bluestone is
2.27. It occurs sparingly in nature, but large quantities
are made artificially, for filling the kind of electric batteries
used in telegraphy.

The farmer has found uses for bluestone. Seeds of wheat,
rye and other grains are often moistened with a dilute solution
of it before sowing. This prevents "smut," which means
decay of the seed caused by fungi. The Bordeaux mixture,
so widely used as a fungicide, is a paste, made by mixing
bluestone and slaked lime.

The chemical nature of bluestone can be investigated in
the following way:

1. The barium chloride testy applied to a solution of the
crystals, shows that they consist of a sulphate.

2. When the crystals are heated in a current of hydrogen or
illuminating gas, a pink mass of copper is left.

From (1) and (2) it follows that bluestone is copper sul-
phate.

3. By heating bluestone in a dry test tube it can be shown
that the crystals contain water. Quantitative work shows

SULPHURIC ACID AND ITS SALTS 281

FiQ. 85. — ^Electrolysis of copper sulphate.

that there are five molecular weights of water to one of cop-
per sulphate, so that the formula is CUSO4 5 H2O. This
water is called water of crystallization. Is it chemically com-
bined, or merely mixed with the CUSO4? In answering this
question the student should consider that the water is present
in a definite proportion, and
that, when it is expelled by
heat, the blue crystals
crumble to a white powder,
and show an abrupt change
in all their properties.

370. Electrolysis of Cop-
per Sulphate. — (a) When
two electric light carbons, connected with the opposite poles
of some source of current. Fig. 85, are dipped into a solution
of copper sulphate, the negative carbon becomes coated

with copper:

Cu — >- Cu.

At the positive carbon a gas escapes, which proves to be
oxygen. The blue color of copper sulphate solution is due
to the copper ions and disappears when they are all removed.
The colorless liquid still answers to the barium-chloride test,
but it tastes intensely sour and the sugar test shows that the

sulphuric acid is now free. We may consider that the SO4
ion has given up its negative charge to the positive carbon
and has at once attacked a molecule of water:

SO4 + HaO — ^ H2SO4 + 0.

(5) Let us now use two weighed bits of clean sheet copper, in-
stead of the carbons, in the electrolysis of copper sulphate solu-
tion. Copper deposits at the cathode as before, but no gas bub-
bles from the anode. Finally, the liquid shows no loss of color.

When the copper plates are weighed again, after the elec-
trolysis, the cause becomes clear. The anode has lost just

as much as the cathode has gained. For every Cu which gave

282 AN INDUCTIVE CHEMISTRY

up its charge at the cathode and became ordinary copper, a
copper atom took up a chai^ at the anode and became an

++
ion, Cu. The number of copper ions in the liquid remains
the same. It is as though copper had simply been trans-
ferred through
the liquid, from
the positive to
the negative
plate.

371. IndnBtrlal
AppUckOoiu.— The
principle of these
two experiments is
applied in several

Fio. 88. — The eleotrio refinine of copper, important proc-

1. In electro^IsUng with copper, the object to be pl&ted is hung in a
lead-lined tank, containing a solution of copper sulphate with some free
sulphuric acid, and is connected with the n^ative pole of a dynamo.
"nie anode ia a bar of copper. The principle is eitactly the same as that
of (6) S 370.

2. ElectrotyplnK differs only in the preparation of the object. The
matter is set up in type and a cast of it taken in wan. This is coated
with graphite to make it conduct, and electroplated as in (1). The
result is a reproduction of the original type in copper, which, owii^ to
the graphite, ia easily stripped from the wax. Lead is poured into the
back of the electrotype to strengthen it and it is mounted on a wooden
block. This proceaa ia used for making the platea from which books
aro printed. It is far too alow for newspapers.

3. On account of the large demand for pure copper to make wires for
conducting the electric current, the electric refining of the metal is agreat
industry. The method is simply that of i 370 (b) on a large scale.
The impure copper is cast into plates say 1 m. square X 2 cm. thick,
which are made the anodes in a lead-lined wooden tank containing cop-
per sulphate solution with some sulphuric acid. The cathodes are
plates of pure copper 0.3 m.m. thick. Fig. 86. The liquid is kept in
circulation during the process.

There are two classes of impurities in crude copper: (1) metals more
active than copper, like iron and sine — these dissolve in the bath but
do not deposit on the cathode; and (2) metals less active than copper.

SULPHURIC ACID AND ITS SALTS 283

that is, noble metals, especially gold and silver. Owing to their in-
activity, these latter metals do not dissolve. They remain, coating the
anode and gradually fall to the bottom of the tank, forming a mud.
Their value is great enough to pay the whole expense of the process.
With careful work the purified copper contains less than 0.01% of
impurities.

372. Zinc Sulphate. — Zinc sulphate, ZnS04, is formed when
zinc dissolves in sulphuric acid. It can be made by care-
fully roasting zinc blende:

ZnS + 2 O2 — >- ZnS04.

This method brings out clearly the difference between a sul-
phide and a salphate. The sulphates of copper, iron andsome
other metals can also be made by oxidizing the corresponding
sulphides.

Like many other salts, zinc sulphate forms several com-
pounds with water, of which the most important is ZnS04
7H2O, colorless crystals called "white vitriol." These are
used in filling electric batteries, in calico-printing, and, in
very dilute solution, as an eye wash.

373. Iron Sulphate. — Ferrous sulphate, FeS04 7H2O, was
the "green vitriol" of the alchemists, who made sulphuric
acid, long before the days of the lead chambers, by heating
ferrous sulphate with sand. It is obtained as a by-product
from the cleaning of iron and steel castings by dipping them
in dilute sulphuric acid ("pickling"). When the "pickle"
is exhausted, it is heated with scrap iron and evaporated,
until the ferrous sulphate separates, on cooling, in green
crystals. It is used in calico-printing. Its solution is a
good disinfectant for drain-pipes, for cement floors, or for
anything which can be treated with it without injury.
Ferrous sulphate is often called copperas,

374. Ink. — Gallic add is a compound of carbon, hydrogen
and oxygen closely related to pyro-gallol. It is contained in
nvi galls, and dissolves when they are powdered and treated
with water. This liquid remains colorless when a solution
of ferrous sulphate is added, but when the mixture is exposed

284 AN INDUCTIVE CHEMISTRY

to air, oxy^n is absorbed and a fine, deep black precipitate,
vrhich is the iron salt of gallic acid, appears.

This behavior is the basis of the manufacture of ink. A
little hydrochloric acid improves the keeping quaUties, and
a little gum prevents the iron gallate from settling. A trace
of mercuric chloride or carbolic acid is added to prevent
mould. A small quantity of some greenish or bluish dye is
introduced to make the writing visible when
the ink is fresh.

375. Calcium Sulphate. — The mineral gyp-
sum occurs in flat transparent crystals (Fig. 87),
which are soft enough to be scratched with the
fmger-nail. A compact white form is found
in extensive beds.

The orange flame color shows that gypsum
is a calcium compound, while the barium chlo-
ride test, applied to a solution of the mineral
. hydrochloric acid, proves it to be a 'svl-
ph(Ue. When a bit of the mineral is heated in a dry test-
tube, waier condenses in the upper part of the tube. The
percentage of water can be determined by heating a weighed
quantity to redness in a crucible, and weighing again. The
results of this, and of other quantitative experiments, show
that the formula of gypsum la CaSO* 2H2O.

376. "Plaster of Paris." — When powdered gypsum is heated
to a temperature not exceeding 200', three-fourths of the water
escapes, leaving a white powder of the formula 2CaS0<H,0.
This is called "plaster of Paris" because it has long been
made at the gypsum quarries of Montmartre, near Paris.

When water is added to plaster of Paris, the lost water is
taken up again and CaSOi2HjO is again produced, as a hard,
compact mass. The making of plaster casts depends upon
this fact. The plaster expands a little on becoming solid
and therefore gives a sharp impression of the mould. Plaster
is too weak and too soluble in water to be used in outnioor
work.

UloC gypeum.

SULPHURIC ACID AND ITS SALTS . 285

If the gjrpsum is somewhat overheated, so that all the water is driven
out, the plaster is spoiled, for it will not "set" with water. However,
if the gypsum is thoroughly heated to bright redness (lOOO**), a yellowish
white powder (CaS04) is formed, which, when mixed with one-third of
its weight of water, slowly hardens to a stony mass.

377. Barium Sulphate. — Bariuv} sulphate, BaS04, is the
white, "insoluble" powder obtained in testing for sulphuric
acid with barium chloride. 100 c.c. of water dissolves only
0.0002 gram of it, which explains why the precipitate ap-
pears, even in very dilute solutions of sulphates. It is found
abundantly as the mineral heavy spar which often occurs with
ores of lead.

Barium sulphate is often called barytes. It is employed as
a "filler" for heavy paper, tod is a frequent adulterant in
paint.

378. Potassium Sulphate. — Potassium sulphate, K2SO4,
forms colorless crystals, which contain no water. It is made
at Stassfurt by mixing solutions of magnesium sulphate and
potassium chloride:

MgS04 + 2 KCl —9- MgCU + K2SO4.

It is much less soluble than magnesium chloride and there-
fore crystallizes before the latter when the liquid is eva-
porated. Like potassium chloride, it is widely employed as
a fertilizer, to supply potassium to plants. It is also used
in making alum.

379. Magnesium Sulphate. — Magnesium sulphate, MgS04

7H2O, forms colorless crystals which have long been used

in medicine under the name Epsom salt. It is very soluble

in water.

Magnesium is a grayish white metal of specific gravity 1.7 which
melts at a dull red heat (750**). It is rapidly dissolved by the ordi-
nary acids. Heated in the air, it burns, with a brilliant flame, to white
magnemim oxidey MgO, which is often called magnesia. The chief use
of magnesium is in making flash-light powder*

286 AN INDUCTIVE CHEMISTRY

380. The Sulphates of Sodium. — Either one or both of the
hydrogen atoms of sulphuric acid can be replaced by sodium.
The two possible sulphates are:

Sodium hydrogen sulphate, NaHS04
Sodium sulphate, Na2S04.

Sodium hydrogen sidphdte can be made by treating a solu-
tion of 98 grams (one molecular weight) of sulphuric acid
with 40 grams (one molecular weight) of sodium hydroxide
and evaporating:

NaOH + H2SO4 — >- NaHS04 + H2O.

If 98 grams of sulphuric acid are mixed with a solution of
80 grams (two molecular weights) of sodium hydroxide,
sodium sulphate is obtained on evaporation:

2 NaOH + H2SO4 —>- Na2S04 + 2 H2O.

Sodium sulphate Na2S04 is often made by treating rock
salt with sulphuric acid, the mass being finally brought to
a red heat:

2 NaCl + H2SO4 —>- Na^04 + 2 HCl.

Its great use is in glass-making.

The crystala of sodium sulphate which are formed from a water solu-
tion have the composition Na«S04 10 H2O. Their conduct with water
is a striking instance of supersaturated solvtion (p. 209). 100 c.c. of
water at 20® take up from these crystals a quantity which corresponds
to 20 grams of Na2S04. At 34° the quantity dissolved corresponds to
about 80 grams Na2S04.

If the solution, saturated at 34®, is freed from all undissolved matter,
it may be cooled and kept for a long time without crystallizing, but if
a crystal of sodium sulphate is dropped into it, a mass of crystallized
Na^SOi 10 H2O separates at once.

381. Aluminium Sulphate. — Aluminium sulphate, Al2(S04)3,
forms white crystals with 18 H2O, which dissolve in about
their own weight of cold water. It is often made by
boiling clay (which is an aluminium compound) with sul-
phuric acid. More often it 19 made by the action of sulphuric

SULPHURIC ACID AND ITS SALTS 287

acid upon bauxite which is a mineral composed of
aluminium oxide and water. Bauxite occurs in Arkansas,
Georgia and Alabama. The powdered mineral is boiled with
chamber-acid in a great lead lined cauldron, and the solution
allowed to solidify to a crystalline cake of Al2(S04)8l8 H2O.
Aluminium sulphate is an important substance. It is
used in sizing paper, in making cloth water-proof, in fire-
proofing wood, and as a mordant in dyeing.

382. Alum. — ^We have met with many cases of the imion of two ele-
ments to form a compoimd. Can two compounds do the same thing?
Can they combine with each other to form a more complex compomid?
Compounds like CUSO4 5 H2O, ZnS04 7 H2O, etc. compel us to admit that
this fonn of combination is of frequent occurrence. We must now in-
quire whether two aaUa can unite to form a more complex salt which
contains them both.

When a strong solution of aluminium sulphate is mixed with one of
potassium sulphate, a crop of colorless octahedral crystals appears.
When analyzed) these prove to contain a molecular weight of each of
the sulphates'

KjSO* AliCSO*).

and, in addition, 24 molecular weights of water. This double aaU is
called alum. It is used as a mordant in dyeing. Of late it has been
largely displaced by almninium sulphate, which answers the same pur-
pose and is cheaper. Alum is still used for mordanting delicate colors
because it can easily be purified, while aluminium sulphate is apt to
contain a little iron, which may alter the shade. Alum is also employed
in tanning glove-kid and other light leather.

The sulphates of other imivalent metals form similar compounds with
aluminium sulphate which are also called ''alums.''

Sodium alum, NazSOi Alt (804)3 24 HsO, is becoming an important
salt in dyeing. Other trivalent metals Uke chromium^ Or, may take the
place of the aluminium, forming salts which, though they contain no
aluminium, are called alums. Chrome cdum^ KSO4 Cri(S04)s 24 HsO, is
a plum-colored salt. It is often added to the "h3rpo" fixing bath in
photography, to harden the gelatin film.

The alimis all crystallize in octahedra, and contain twenty-four mole-
cules of water. They are quite nimierous. Thousands of other
double saUa are known.

383. Ammonium Sulphate. — Ammonium sulphate^
(NH4)jS04, forms colorless crystals, which dissolve in twice

288 AN INDUCTIVE CHEMISTRY

their weight of water. It is made by distilling the ' 'ammoniacal
liquor" from the gas-works and coke-ovens and leading the
ammonia, which escapes, into dilute sulphuric acid:

2 NH, H- H,S04 ^ (NHO^SO*. .

The total annual production of ammonium sulphate is
nearly a miUion tons, and this could be greatly increased if
all coke were made in ovens in which the by-products were
properly collected. Its great use is as a fertilizer, to supply
nitrogen to crops.

Sodium sulphite, NatSOs 7 HtO, forms white crystals, soluble in water.
Added to the developer in photography, it acts as a preservative, retard-
ing the spoiling of the solution by tJ^sorption of oxygen. The sulphites
of most metals are insoluble in water.

Sodittm thiosulphate, Na«SsOt 5 HsO, forms colorless, very soluble
crystals. It is the "hypo" of the photographer. It is largely used
in paper-making.

Related Topics

384. The Colors of Ions of the Metals.— Copper sulphate,
CuSOi, is white; its dilute water solution is blue. This color is

not due to the SO4 ion, for we know from the solutions of sul-
phuric acid, and many sulphates, that this ion is colorless. The

++
blue color must be due to the ion Cu.

Copper chloride CuCU is brown. Its solution in alcohol is
bright grass-green and does not conduct the electric current,
but its dilute water solution conducts and has exactly the same
blue color as a solution of copper sulphate.

The important thing to notice here is the way the facts sup-
port the idea of ionization. Since the water solutions of copper
chloride and sulphate conduct the electric current, they must

contain the ion Cu. The identical color in the two liquids is an

independent proof of the presence of the same ion Cu in both.

Cobalt (Co) is a metal so similar to nickel that it is sometimes
used for "nickel" plating. It is bivalent, so the ion must be

Co.

HYDROLYSIS 289

Cobalt chloride, CoClt, is blue, and so is its alcohol solution,
which is a non-conductor. The water solution conducts and

has a delicate rose-pink tint. This must be the color of the Co ion,
for chlorine ions are colorless as we know from solutions of table-
salt and of hydrochloric ac d.

Cobalt nitrate is brown; the alcohol solution has the same color
and does not conduct. From both facts we conclude that it
contains un-ionized molecules Co(N08)t. The water solution is

a good conductor, showing that the molecules have broken into

++ -

ions Co and 2N08, and it has exactly the same rose color as a

water solution of cobalt chloride.

++
This striking difference of color between Co and CoCU is the

basis of sympathetic ink. The pink dilute solution of cobalt

chloride, the color of which is due to Co, is invisible on white paper
when used as an ink. When the paper is warmed, the water is
driven off and the writing appears in blue, owing to the formation

of C0CI2 .

A rather untrustworthy way to foretell the weather can be
based upon the same fact. The instrument is a rag which be-
comes blue for fair weather and pink for rain. The rag has been
dipped in a solution of cobalt chloride. When the air is dry
the water evaporates and leaves blue CoCU, but when there is
much water vapor in the air (indicating rain) the C0CI2 absorbs

water and pink Co is formed.
385. Hydrolysis. — We have seen (p. 256) that when hydrogen

ions H come into contact with hydroxyl ions OH, water is in-
stantly formed:

+ . —

H + OH — >• H,0.

This is what really happens when an acid and a base
neutralize each other.

We must now inquire whether this Combination is complete

+ —

or whether it is possible for a few H and OH ions to exist to-
gether in a liquid without combination. In other words, is
perfectly pure water all composed of molecules H2O, or are there

290 AN INDUCTIVE CHEMISTRY

some hydrogen and hydroxyl ions scattered among the un-ionized

molecules?

The plain way to get knowledge on this matter is to prepare

pure water and see whether it conducts the electric current. If it

+ —

does, it must contain traces of H and OH. The purest water ever

obtained was made by KoKLrauach, by repeated distillation in a
vacuum. He found that, although a very bad conductor, the
water did conduct a little. Imagine a cylinder of Kohlrausch's
pure water one meter long and having, as the area of its base, Isq.
centimeter. Such a cylinder would offer about the same re-
sistance to the current as a copper wire of the same cross-
section, long enough to go around the earth at the equator
300,000 times.

From this very slight conducting power, it can be calculated

+
that, in round numbers, there are one gram of H ions and 17

grams of OH ions in 13 miUion liters of water. This may seem
too small a concentration to amount to anything, but we must
reflect that, owing to the smallness of the atoms, it corresponds
to a very large number of ions. Though they are few in com-
parison to the un-ionized water molecules, the ions, even in pure
water, are so numerous that they are only about 0.001 m.m.

apart on the average. We shall see at once that this slight

+ —
ionization of water into H and OH produces some interesting results.

A solution of copper sulphate reddens blue litmus paper: there-

fore it must contain more H ions than pure water, which does

not. Whence do these extra H ions come?

The water is the only possible source of them; more of it must
break up into ions when copper sulphate is dissolved in it; but
why?

Copper hydroxide Cu(0H)2 is a very inactive hase^ that is, it
exists almost altogether as molecules, and hardly at all as ions

Cu and OH. When copper sulphate is dissolved in water, the

++^

Cu ion has many OH ions offered to it, and they unite to mole-

cules Cu(0H)2. This cuts down the number of OH ions so that

HYDROLYSIS 291

there are no longer 17 grams of them in 13 million liters and more

+ —

of the water molecules break up into H and OH. These new

OH ions unite with the Cu ions and so on. The H ions become

more and more numerous, until finally there are enough of them

to redden the litmus. We may say that copper sulphate solution

+
contains a Uttle free sulphuric acid, for it contains H ions from the

water and SO4 ions from the copper sulphate.

On the contrary, a solution of sodium sulphide, NajS, turns red
litmus blue. Hydrogen sulphide, HjS, is a very inactive acid
which exists almost wholly as un-ionized molecules when dis-
solved in water. When sodium sulphide is dissolved it separates

into 2Na and S. The sulphur ion S findsvnumerous H ions

ready to unite with it and HtS molecules are formed. The OH
ions, which are left, become abundant enough to turn the red
litmus blue.

A solution of table-salt has no effect on either red or blue
litmus. Both sodium hydroxide and hydrochloric acid are very
active, that is, almost completely ionized. Hence there is no

imion either of Na and OH or of H and 01 and the nimiber of H and

OH ions remains the same as in the pure water.

These are merely examples. It may be left as an exercise to
the student to show from them that:

(1) A salt of an active acid with an inactive base will redden
blue litmus. Examples: copper sulphate, chloride and nitrate,
aluminium sulphate.

(2) A salt of an active base with an inactive acid will turn red
litmus blue. Examples: sodium sulphide, sodium cyanide (p.
210), washing-soda (sodium carbonate), borax (sodium borate).

(3) A salt of an active acid with an active base will not change
the color of either kind of litmus. Examples: sodium chloride,
nitrate and sulphate and the same salts of potassium and calcium.
All these instances can be quickly tested in the laboratory.

(4) The chemical equ9,tion for the hydrolysis of a salt is merely
the equation for the neutralization of the corresponding acid and
base, read backward. Hydrolysis is the reverse of neutralization.

292 AN INDUCTIVE CHEMISTRY

386. Electrolysis of Water. — When water is placed in the
apparatuiB of Fig. 88, and the electric circuit completed, no gas
escapes at either electrode because the resistance of the water
is so great that hardly any current passes. But if a little so-
dium sulphate, NaiSOi, is dissolved in the water the current passes
at once : oxygen escapes at the anode
and twice as much hydrogen by
volume at the cathode.

The current did not pass through
the water, because there were not
enough ions to carry it. It does
pass through the sodium sulphate
solution, because the innumerable
+

Na ions carry the positive elec-
tricity to the cathode while the SO.
Flo. 8s.— The eiBotrDiyng of wat«t. ions Carry the negative electricity
to the anode. So much is clear.
But what happens at the cathode? Hitherto we have assumed
in such cases (p. 244) that the sodium ion gives up its charge
and is changed for an instant into sodium metal, which inter-
acts with water:

Na + HiO — >■ NaOH + H (I)

That view served a good purpose as a beginning. We want now
to penetrate more deeply into the matter.

Is there any proof that sodium ions are discharged at all? A
crowd of positive ions ia pulled to the cathode by its negative
charge. This crowd consists mainly of sodium ions, but there
are miUions of hydrogen ions in it from the water. The hydrogen
ions lose their charges far more easily than the sodium ions, so thoy
give up their poative electricity to the cathode and form hydrogen
gas:

2H — >■ Hi

The part played by the sodium ions is merely to carry the posi-
tive electricity through the liquid.
The same fact holds true for the anode. The work of carrying the

negative electricity to it is done mainly by the SOt ions, but in

ELECTROMOTIVE SERIES 293

the army of negative ions which are drawn to the anode are

multitudes of hydroxyl ions OH, from the water. These lose

their negative electricity much more easily than the SO4 ions
so they do lose it, and oxygen escapes:

2 OH —>- H2O +

As the electrolysis goes on, fresh molecules of water are al-

+ —

ways breaking up into H and OH so that the concentration of

both always remains the same.

As this experiment is commonly carried out on the lecture

table, sulphuric acidy instead of sodium sulphate, is added to the

water. The result at the anode is exactly the same as when sodium

sulphate is used. At the cathode, matters are still simpler. Multi-

tudes of H ions collect there, are discharged and converted into
hydrogen gas. It makes no difference whether they come from the
water, or from the acid.

387. The Electromotive Series of the Metals. — When a strip
of zinc is placed in a solution of copper sulphate, or any other
soluble copper salt, a red deposit of copper is produced upon the
zinc. At the same time, zinc dissolves:

CuSOi + Zn -^ ZnSOi + Cu

++ ++

or, better, Cu + Zn — >- Cu + Zn

Copper ion zinc metal copper metal zinc ion

A strip of silver y however, is not coated with copper when
dipped into a solution containing copper ions. On the contrary,
when copper is placed in a solution containing silver ions, silver
is deposited upon the copper. Since silver is univalent, the
equation is:

+ ++

2Ag + Cu — >- 2Ag + Cu

Silver ion Copper metal Silver metal Copper ion

Zinc, placed in a solution containing silver ions, becomes
coated with silver:

+ ++

2Ag + Zn — >• 2Ag + Zn

Silver ion Zinc metal Silver metal Zinc ion

294 AN INDUCTIVE CHEMISTRY

Thus, if we arrange these three metals in the following order:

Zinc

Copper

Silver

we can say that each metal precipitates those which follow it and
IS precipitated by those which precede it. When all of the
important metals are included in an investigation of this sort,
the resulting arrangement is known as the electromotive series.
It is as follows:

The Sodiimi Group Tin

The Calciimi Group Lead

Magnesium HYDROGEN

Aluminium Copper

Manganese Antimony

Zinc Bismuth

Chromium Mercury

Cadmium Silver

Iron Platinum

Cobalt Gold
Nickel

Any metal in this series will precipitate metal from a solution
containing ions of any of the metals which follow it, but will not
affect a solution containing ions of a metal preceding it. The
metals preceding hydrogen hberate hydrogen gas from solutions
containing hydrogen ions, that is from adds; those which follow
hydrogen do not. Since water itself contains hydrogen ions, the
metals preceding hydrogen rust in contact with water, and, for this
reason, are hardly found in the free state in nature: those following
hydrogen scarcely rust and are therefore found native, although
most of them also occur as compounds. The student will note
that chemical activity decreases as we descend the table, the sodium
group being intensely active, while platinum and gold are the most
inert of the metals.

We have seen that galvanized iron resists the action of the weather
much better than iron plated with tin. The electromotive series
explains this fact. Since zinc precedes iron, water will have no
action upon the iron until the zinc has all rusted. On the other
hand, iron precedes tin and therefore the iron rusts first when iron

ELECTROMOTIVE SERIES 295

and tin are exposed together to water. Hence the protection
afforded by tin against rusting lasts only as long as the plating of
tin over the iron remains imperforated.

Definitions

Anhydride. An oxide which combines with water, producing
an acid.

Hydrolysis. The interaction of a salt with watetf producing an
add and a base. Hydrolysis is merely the reverse of neutraUzation.

CHAPTER XXIII

NITRIC ACID AND ITS SALTS.— COMPOUNDS OF NITRO-
GEN AND OXYGEN.— CHLORIC ACID AND ITS SALTS

388. Chili Saltpeter. — In the province of Tarapaca^ which
occupies the almost rainless part of northern Chili, between
the Andes and the Pacific, are found great beds of a mineral
called Chili saltpeter.

When pure, the mineral forms transparent, coioriess crys-
tals, very soluble in water, but it is commonly found in
masses colored gray, brown or yellow. That it is a sodium
compound is clear from the intense yellow which it gives to
the flame. When some of the mineral is heated in a glass
tube it gives off a gas which the spark test shows to be
oxygen. When the powdered mineral is mixed with about ten
times its volume of iron powder, and heated, a gas escapes
which can be collected over water, and shown to be nitrogen.
Finally, if the mineral is gently warmed with a Uttle sulphuric
acid, a vapor escapes which, when condensed to a liquid,
proves to be nitric acid, HNOs. Chili saltpeter is the
sodium salt of nitric acid; it is sodium nitrate, NaNOs.

389. The Production of Sodium Nitrate. — In Chili, the crude
mineral is treated with boiling water in iron boxes, and the
solution of the sodium nitrate, freed from insoluble impurities,
is allowed to crystallize. This product, which contains
about 95% of sodiiun nitrate, is shipped to the United
States and to Europe. Considerably more than a billion
dollars worth of sodium nitrate has been obtained from
the Tarapaca beds, and it is claimed that enough re-
mains to .supply the demand for two centuries or more.
It is being exported at the rate of nearly two million
tons a year. Much of it goes on the soil, as a nitrogen
fertilizer, and the rest chiefly into the manufacture of
nitric acid

296

NITRIC ACID AND ITS SALTS

297

390. Nitric Acid : Preparation. — Nitric add, HNOs, is made
by gently heating sodium nitrate with sulphuric acid:

NaNOs + H2SO4

NaHS04 + HNO3

The mixture is contained in a horizontal iron cylinder
(Fig. 89), which will take about five tons of the nitrate, and
rather more than that quantity of sulphuric acid (chamber-
acid). The vapor is condensed in a series of stoneware
bottles.

Any nitrate will yield nitric acid with sulphuric acid. Sodium nitrate
is used because it is cheap. Sulphuric acid is chosen for the same rea-
son, and also on account of its high boiling-point. When sulphuric

Fig. 89. — ^The manufacture of nitric acid,

acid and sodium nitrate are mixed in the cold, there is a partial inter-
action: sodium hydrogen sulphate and nitric acid are formed, until their
concentration becomes great enough to prevent the change from going
any further. But when heat is applied, the nitric acid is removed, as
vapor, so that its concentration is kept below the limiting value, and the
change goes on to completion. Taking into account that sulphuric
acid boils at 338° and nitric acid at 86°, could sulphuric acid be made
by distilling sodium hydrogen sulphate with nitric acid?

391. Properties of Nitric Acid. — Pure nitric acid is a color-
less liquid about one and a half times as heavy as water.
It boils at 86° and freezes at -50°. The concentrated nitric
acid of the laboratory contains 68% of HNOs, the rest being
water, which reduces its specific gravity to 1 . 41.

The student has probably noticed that the nitric acid in
the bottles which stand near the windows, in strong light,
is red. Some of the acid is decomposed by light:

2HNO3

H2O + 2 NO2 + O

298 AN INDUCTIVE CHEMISTRY

and the nitrogen peroxide dissolves in the rest and colors it.
The same decomposition occurs when the acid is heated, and
gives some trouble in its manufacture.

Nitric acid is evidently an unstable substance. The
formula HNOj shows that it contains H of its weight of
oxygen, which is more than three-fourths. Putting these
two facts together, it is reasonable to expect that the acid
will prove to be a violent oxidizing agent, for all this loosely
held oxygen will be offered freely to any substance which
will accept it. There are 800 liters of oxygen in a liter of
pure nitric acid.

It is not surprising, therefore, that nitric acid may set
fire to the hay, straw and sawdust which are often used in
packing bottles, and that it must be packed for transporta-
tion with special care. Its action upon clothing is another in-
stance of oxidation. A flame of illuminating gas goes on
bummg when plunged under the surface of pure nitric acid.
So does a bit of charcoal, which has been heated to redness
in the air. The warm vapor of nitric acid responds to the
spark test.

Nitric acid is one of the most active acids known. The
name which the alchemists gave to it, aqiui fortis, refers to
this fact. Its behavior with bases is similar to that
of hydrochloric acid and has already been briefly dis-
cussed.

392. Action of Nitric Acid on Metals. — Nitric acid does
not affect platinum or gold. Most of the other familiar
metals, like iron, zinc, copper, lead, silver and mercury, are
rapidly dissolved as nitrates. The last four are hardly at-
tacked by hydrochloric or dilute sulphuric acid.

The equations for the interaction of nitric acid with metals are dif-
ficult to write. This is because the acid acts not only as an addy but
also as an oxidizing agent. The essential thing about the interaction of
an acid and a metal is that hydrogen escapes and the atom of the
metal is taken into the solution instead. In the case of nitric acid,
however, this hydrogen does not escape. It is oxidized to water by an-
other molecule of nitric acid and this action produces complications, as

NITRIC ACID AND ITS SALTS 299

can be seen from an example: Zinc is rapidly converted into zinc ni-
trate, Zn(N03)2, by moderately concentrated nitric acid, but no hydro-
gen escapes — the gas given ofif is red nitrogeii peroxide NO2. We may
assume that, for an instant, hydrogen is Hberated as usual:

Zn H- 2 HNO, >- Zn(N0,)2 + 2 H (1)

but is oxidized at once by more nitric acid:

H + HNOs — >- H2O + NO, (2)

If the nitric acid is diluted with five times its volume of water, zinc
nitrate is formed as before (1) but no nitrogen peroxide escapes. The
gas formed is colorless nitric oxide, NO. Three atoms of hydrogen have
attacked one mo ecule of nitric acid:

3 H + HNO3 — >■ 2 H2O + NO (3)

Nitric oxide also escapes when copper dissolves in dilute nitric acid,
the equations being similar to (1) and (3).

The two steps can be combined in one equation, which may be needed
in solving numerical problems. When copper dissolves in nitric acid
we have:

3 Cu + 8 HNOs — >■ 3 Cu(N08)2 + 4 H2O + 2 NO

In the case of tin, and some other substances, the acid acts chiefly
as an oxidizing agent. The product, when dried by heat, consists of
tin dioxide:

Sn + 4 HNOs — >- SnOz + 2 H2O + 4 NO2.

393. Uses/of Nitric Acid. — Nitric acid is made in large
and increasing quantities. The chief use of the concentrated
acid is in the manufacture of high explosives, like nitroglyce-
rine and guncotton (Chap. XXVIII). The dilute acid is used
in the preparation of the copper-plates from which etchings
are printed, in making silver nitrate, ammonium nitrate and
other nitrates, and in dissolving metals. From an alloy of
gold and silver not too rich in gold, it dissolves out the silver,
leaving the gold. It was formerly used in mints for the sepa-
ration of these two metals, but hot concentrated sulphuric
acid, which acts in the same way and which is cheaper, dis-
placed it. The separation of gold and silver in mints is now

300 AN INDUCTIVE CHEMISTRY

carried out by an electrical method, similar in principle to
the refining of copper.

394. The Nascent State. — ^We have just seen that hydrogen, gen-
erated in a liquid containing nitric acid, is not permitted to escape, but
is oxidized to water. But if the hydrogen is made in another vessel
and passed into dilute nitric acid through a glass tube, it bubbles
through the hquid without change.

If silver chloride, AgCl, is suspended in water and hydrogen is passed
into the water there is no effect, but if zinc and hydrochloric acid, or
any mixtiu^ which can generate hydrogen, are added to the same
liquid, the silver chloride is rapidly converted into metal:

AgCl + H — >- HCl + Ag

It seems from these, and many similar instances, that hydrogen, at
the instant of its liberation, before it has taken form at all as a gas, is
more oc^ ye th n hydrogen gas already formed

The atomic theor suggests, as an explanation, that the hydrogen is
first Uberated as single atoms. When these imite to form the molecules
Hi of hydrogen gas, they become less active, because the bond be-
tween the two must be ruptured before any chemical action can occur.
Perhaps the chief value of such a hypothetical explanation is that it
helps us to remember the fact that not only hydrogen but many other
elements are more active in the moment of production — ^in the nascent
state, as it is called — than they are afterward.

Some powdered metals, like platiniun absorb hundreds of times
their volume of hydrogen and these solid solutions are able to produce
many of the effects of nascent hydrogen. This fact is in direct conflict
with the above explanation. In these cases, the greater activity is
clearly due to the greater concentration of the hydrogen.

395. Aqua Regia.-:— A mixture of nitric and hydrochloric
acid is called aqtui regia. It dissolves gold and platinum,
which are not acted upon by either acid singly. The reason
is that the nitric acid oxidizes the hydrogen of the hydro-
chloric acid to water, liberating chlorine. The nascent
chlorine converts the metal into chloride, which dissolves.

396. Salts of Nitric Acid. — The formula of nitric acid
shows that the radical NO3 is univalent. Hence the for-
mulas of the nitrates can be written at once if the valence
of the metal is known. Some examples will make this clear.
The only unfamiUar substance in the list is thorium nitratef

NITRIC ACID AND ITS SALTS 301

which is a white solid, much used in making Welsbach
mantles.

Metal

Valence

FonmUa of Nitrate

Potassium

KNO,

Calcium

CaCNOa),

Aluminium

A1(N03).

Thorium

Th(N03)i

The nitrates are all freely soluble in water. The ion NOs
is colorless.

397. Potassium Nitrate. — Potassium nitratef KNO3, is
commonly called "nitre," or "saltpeter." It forms colorless
prisms which contain no water of crystallization. To make
it, Chili saltpeter andStassfurt potassium chloride are placed,
with a limited quantity of water, in a steam-heated iron
vessel:

NaNOa + KCl — ^ KNO3 + NaCl

In an hour, most of the sodiiun chloride has separated, and

the liquid is filtered through canvas to remove it. When the

liquid is allowed to cool in another tank, the potassium

nitrate crystaUizes.

The principle of the method will be clear from a glance at the solu-
bility curves of table-salt and nitre (Fig. 74). The solubility of table-
salt is scarcely increased by heat, and it separates in the hot liquid be-
cause there is not enough water present to dissolve it. The nitre re-
mains dissolved so long as the liquid is hot, because of its great solu-
bility at higher temperatures, but crjrstallizes on cooling, on account of
the great reduction in its solubiUty.

398. Black Gunpowder. — Potassium nitrate finds its
main use in the manufacture of black gunpowder. This is
a mixture containing, by weight, about 6 parts potassium
nitrate, 1 part charcoal, and 1 part sulphur. The materials
are finely powdered separately, mixed, and granulated. It
is still largely used for hunting and saluting. In warfare,
it is obsolete.

We may write a simplified equation for the explosion of gimpowder:

2 KNOs + 3 C + S — >• K2S + 3 CO2 + Ni

302 AN INDUCTIVE CHEMISTRY

The chemistry of the explosion is really quite complicated, but this
simple equation will help us to remember that the nitre serves as a
source of oxygen to bum the carbon, and that the nitrogen escapes as
gas. In fact, the sudden formation of gas is really the cause of the
explosion. The gases from 1 c.c. of powder would occupy, at S.T.P.,
about 500 c.c. and this volume is vastly increased by expansion, due to
the high temperature. Since this sudden expansion requires only a
small fraction of a second, the reason for the effects of the explosion is
plain.

It would be a mistake to conclude from these effects that gimpowder
contains more energy than ordinary fuels, for the direct reverse of this is
true. One gram of gunpowder when burned yields about 600 cal.,
while one gram of the best coal gives about 8000 cal. Hence if war-
ships were driven by engines which burned gunpowder, their f uel-bimkers
would have to be made more than a dozen times as large as at present.
The point is not that so much energy is evolved in the explosion of gun-
powder, but that energy is evolved so quickly.

399. Silver Nitrate. — Silver nitrate, AgNOs, forms flat
colorless crystals, very soluble in water. It is made by dis-
solving silver in nitric acid. When heated, the crystals
melt and, at a higher temperature, decompose, leaving a
residue of silver.

When silver nitrate gets upon the hands, the organic
matter of the skin converts it into silver, which produces a
black stain. The same action occurs in linen or cotton goods,
so that a solution of silver nitrate is used as indelible mark-
ing-ink. Silver nitrate is employed in medicine as " caustic "
for the removal of warts, etc. Its chief use is in the manu-
facture of photographic plates and films (p. 269).

400. Ammonium Nitrate. — Ammonium nitrate, NH4NO8,
forms colorless crystals very soluble in water. If the water
is stirred with a thermometer, it is foimd that the dissolving
of the ammonium nitrate is accompanied by a decided fall in
temperature. If the beaker is stood upon a wet block of
wood, while the ammonium nitrate is dissolving, the block
will be frozen to the bottom of the beaker.

As a rule, although there are marked exceptions, the formation of
solutions of solids in liquids absorbs heat.

COMPOUNDS OF NITROGEN AND OXYGEN 303

Ammonium nitrate is made by distilling the ammonia-
liquor obtained as a by-product of coke-ovens and gas-works,
and leading the ammonia gas which escapes into nitric acid:

NH3 + HNO3 —>- NH4 NO3.

The fire-damp (p. 181), which causes so many accidents in soft-coal
mines, can be ignited not only by the flames of the miners' lamps, but
also by the blasting necessary to bring down the coal. The main use
of ammonium nitrate is in the manufacture of "safety explosives,'' that
is explosives which are not likely to ignite fire-damp. Explosives of
this sort are often made by mixing powdered ammonium nitrate with
combustible substances like naphthalene, rosin, sulphur or even flour.
They also possess the great advantage of not being sensitive to shock,
so that they can be handled and transported without danger.

401. Nitrous Oxide. — ^When ammonium nitrate is heated
it first melts and then decomposes:

NH4NO3 — >- 2H2O -h N2O

nitrous
oxide

Nitrous oxide is a colorless gas, which dissolves in about
its own volume of water at room temperature. Like all gases,
it is less soluble in hot water. Priestley discovered it, and
Sir Humphry Davy found that, when inhaled, a little pro-
duced intoxication (hence the name, "laughing gas"), while
more caused the subject to become insensible for a short
time. This latter effect has caused it to be widely used by
dentists, who purchase it liquefied in steel cyUnders.

Like oxygen, nitrous oxide gives the spark test. Unlike
oxygen, nitrous oxide does not unite completely with sub-
stances which are burned in it. A volume of nitrogen equal
to that of the nitrous oxide is left.

The nitrous oxide required to fill our standard cube of 22 . 4 liters at
S.T.P. weighs 44 grams. Let all the oxygen be removed, from this
amount of the gas, say by burning iron to iron oxide in the gas. Then
22.4 Kters of nitrogen will remain which will weigh (p. 109) 28 grams or
two atomic weights (N2) . The 16 grams of oxygen which have com-
bined with iron represent one atomic weight (O). Hence the formula
is N2O.

304

AN INDUCTIVE CHEMISTRY

402. Nitric Oxide. — Nitric oxide, NO, may be made by
dissolving copper in dilute nitric acid. It is a colorless,
poisonous gas, slightly soluble in water. The oxygen is more
firmly held in it than in nitrous oxide, as can be seen by com-
paring the behavior of the two gases toward combustible
substances:

Combustible

Nitrous Oxide

Nitric Oxide

Splinter bearing sparks

bursts into flame

extinguished

Burning candle

bums with increased energy

extinguished

Sidphvr burning fed)ly

extinguished

Sulphur burning freely

bums with increased energy

extinguished

Phosphorus burning feebly

bums with increased energy

extinguished

Phosphorus burning freely

bums with increased energy

burns ener-
getically

Burning magnesium

bums with increased energy

bums ener-
getically

After combustions with nitric oxide, a volume of nitrogen

equal to one-half that of the nitric oxide is left.

22.4 liters of nitric oxide weigh 30 grams. After the oxygen has
all been removed by heated iron, 11 .2 liters of nitrogen remain, which
weigh 14 grams or one atomic weight (N). The 16 grams of oxygen
which have combined with iron represent one atomic weight (O). Hence
the formula is NO.

403. Nitrogen Peroxide. — ^When a bottle filled with nitric
oxide is opened, the gas at once becomes deep reddish
brown. This is owing to the formation of nitrogen peroxide:

NO +

NO2

nitrogen
peroxide

The injurious action of nitric oxide is therefore really due to
nitrogen peroxide, which is formed as soon as nitric oxide
meets the air.

Nitrogen peroxide is a poisonous gas and is all the more
dangerous because the first effects are not very noticeable.
For this reason the red gas given off when nitric acid acts

CHLORIC ACID AND ITS SALTS 305

upon metals should not be inhaled. Nitrogen peroxide
disappears when shaken with water, but not by mere solu-
tion. A chemical change takes place and nitric acid and
liitric oxide are formed:

3NO2 + H2O — ^ 2HNO3 + NO

Nitrogen peroxide supports combustion brilliantly, for its
oxygen is abundant and loosely held.

404. Sodium Nitrite. — ^When sodium nitrate is carefully
heated one-third of the oxygen escapes:

NaNOa — ^ NaNOz + O
sodium sodium

nitrate nitrite

Sodium nitrite is made by melting sodium nitrate with lead
in cast-iron kettles.

NaNOa + Pb — >- NaNOg + PbO

Since the lead oxide is insoluble and the sodium nitrite very
soluble in water, they are easily separated. The lead oxide is
made into red lead (p. 78).

Most of the metals form nitrites. Sodium nitrite, which
forms pale yellow crystals, is the only one of commercial
importance. It is much used in the manufacture of dyes.
It is now obtained in Norway as a by-product, in the produc-
tion of nitric acid from the air (p. 307).

405. Potassium Chlorate. — Potassium chloraie, KClOs, is
the white salt used in the laboratory in making oxygen. It
is made by passing the electric current through a solution
of potassium chloride, which is stirred constantly:

KCl + 3 H2O —>- KCIO3 + 3 H2

The change takes place in several stages and the equation
merely sums up the final result.

Potassium chlorate forms flat white crystals which con-
tain no water of crystallization. 100 c.c. water dissolves at
0'', 3 grams and, at 100% 60 grams.

306 AN INDUCTIVE CHEMISTRY

The oxygen of potassium chlorate is loosely held. A mix-
ture of the salt with red phosphorus (Chap. XXV) explodes
violently when struck. A crystal of potassium chlorate,
when ground in a mortar with a Uttle sulphur, produces
a series of explosions. The signal caps used on railroads con-
sist of a mixture of sulphur and potassium chlorate contained
in a small tin box shaped Uke a blacking box. A flexible
wire made of lead is attached to the box for fastening it to
the rail.

Potassium chlorate is used in the preparation of dye-
stufiFs, explosives and safety matches. Its solution is excel-
lent as a gargle for an inflamed throat, but, since potassium
chlorate is poisonous, the liquid must not be swallowed.

Sodium chlorate, NaClOs, is a white salt which finds similar
apphcations.

Chloric add, HClOs, is a colorless explosive liquid, which
sets fire to paper and other combustibles.

Related Topics

406. Conyerting the Nitrogen of the Air into Useful Com-
pounds. — Over a million tons of sodium nitrate are used as a fertil-
izer each year, purely on account of the nitrogen
which the salt contains, yet the leaves, and even the
roots, of the plants to which the nitrate is applied are
surrounded by air which contains four fifths of its
volume of nitrogen. Thus the farmer pays a high
price for the very element which blows about by the
cubic mile over his fields.

Fig 90 —A ^^® rcason is that moat plants cannot take up free

clover root nitrogen. They must have it supplied as a nitrate.

with the bac- Plants Can utilize ammonium compounds, because

teria which it •! • •■% • j» j j. -x x • xt

assimilate ni- ^^^ nitrogen IS easily oxidized to nitrates in the
trogen. soll, but free nitrogen is useless to them.

A few plants are exceptions. Clover thrives on
soils which, because the nitrates are exhausted, are barren to
most crops. On the roots of the clover are found small lumps
which contain numbers of a peculiar species of rather large
bacteria (Fig. 90). These oxidize the nitrogen of the air which

JUSTUS VON LIEBIG
i. Qermany, 1803. D, Miinirb. 1

USEFUL COMPOnUNDS OF NITROGEN 307

bathes the roots to nitrates. The nitrates are then absorbed by
the plant.

However, most crops do not share this power of clover, and the
problem of converting the nitrogen of the air into some com-
pound, which can serve as nourishment for them, is one which in-
creases in importance, as the sodium nitrate supply of Chili ap-
proaches exhaustion. The air over a nine-acre field contains
as much nitrogen as the present annual product of the Chilian
beds.

407. Making Nitric Acid from Air. — The production of nitric
add from the air is carried out in three stages:

1. The nitrogen and oxygen of the air are combined to nitric
oxide:

N + O — ^ NO

2. The nitric oxide is allowed to unite with more oxygen:

NO + O — >- NO2

nitrogen
peroxide

3. The nitrogen peroxide is made to interact with water:

3 NO, + H,0 — >- 2 HNO, + NO.

(2) and (3) have been briefly discussed (p! 304), but we have yet
to learn the methods used on the large scale.

1. Whenever air is intensely heated, partial union of the ni-
trogen and oxygen, to form nitric oxide, takes place. The most
effective method of heating is the electric arc and, around an
ordinary arc lamp, traces of nitric oxide are formed. But
if the air is allowed to cool slowly, after passing through the arc,
all the nitric oxide will separate into its elements during the
cooling. The problem, then, is to heat large volumes of air by
means of an arc, and to provide that the air is suddenly cooled,
so that the nitric oxide has no chance to decompose.

The inside of the furnace in which the arc is formed is shaped
like a very flat drum standing on its edge. That is to say, it is
circular, 2 meters wide, 2 meters high and only a few centimeters
thick (Fig. 91). Through the narrow walls which form the edges
of the drum project the electrodes between which the arc
is to burn. They are made of copper and are hollow, so that

308 AN INDUCTIVE CHEMISTRY

they can be cooled by water circulating in the interior. They
approach each other cloaely in the center of the circle, only one
centimeter separating them.

Strong etectro-magnete placed close to the center of the
circle, but outside the furnace, broaden out the arc into a great

Fia. 01. — PTep4nitlDd of nitrje add fiom air.

disc of flame, like an electrical sun, which fills the inside of the
furnace. The air is forced in at the top and air containing
l%by volume of nitric oxide, and having a temperatureof 700°,
leaves the furnace at the bottom.

2. Since the gaees leaving the electric furnace still contain
much oxygen, nitrogen peroxide will be formed from the nitric
oxide as soon as the gases are cool enough to allow it. They
are passed up into large towers built of iron where the nitric
oxide unites with oxygen.

3. The air, which now contains about 1% by volume of ni-
trogen peroxide, is then passed in at the bottom of a granite
tower filled with quartiz pebbles, over which water tridcles.
Here the nitrogen peroxide interacts with the water, forming
nitric acid. Several such towers are in use. By allowing the
water to tricltle through repeatedly, the percentage of nitric acid
in it may be riused to fifty. The nitric acid is converted into
calcium nitrate, Ca CNO.)i, which contains 13% of nitrogen, and

-4

USEFUL COMPOUNDS OF NITROGEN 309

finds ready sale as a fertilizer. It has some advantages over
Chili saltpeter and can be sold at a price to compete with it.
The factory is situated at Notodden, Norway, where there is
abundant water power to generate the electric current. It is a
complete industrial success.

Another type of electric furnace can be used to bring about
the combination of the nitrogen and oxygen to nitric oxide
in the first stage. This consists of a long iron tube in which
an arc 6 meters long burns, between electrodes at
top and bottom (Fig. 92). The air is forced in
at the bottom through a side-tube which has the
direction of a tangent to the surface of the main
tube. The result is that the air acquires a whirling
motion which keeps the arc in the center where the
motion is least. The long thin arc is really a flame
of nitrogen burning to nitric oxide, 2% of which is
contained in the gas which passes out at the top.
It is converted into nitrogen peroxide and nitric
acid as described above.

408. "Nitro-lime" from the Air. — When calcium
carbide, CaCi, is heated in a current of nitrogen a
substance whose commercial name is nitro-lime is
formed:

CaC, + N, — >- CaCNu + C

nitro-lime

The nitrogen is made from the air by Linde's
method (p. 176). Air is liquefied and allowed to
trickle down a tower filled with glass balls. Nitro-
gen gas, nearly pure, escapes at the top, while liquid p^^ 92 —An-
oxygen collects at the bottom. This cheap and other furnace
almost complete separation is due to the fact that for making
nitrogen has a lower boiling-point than oxygen: ^^J*,^*^*
oxygen condenses at a higher temperature.

When the tower is working, the bottom contams liquid oxygen

from the surface of which oxygen gas escapes and ascends among

the glass balls. But it does not get very far for, trickling over

them, it meets liquid nitrogen, whose temperature (-194**) is

lower than the point at which oxygen condenses (-183°). Hence

the oxygen becomes liquid and flows down, while an equivalent
21

310 AN INDUCTIVE CHEMISTRY

amount of nitrogen becomes a gas and moves upward. We have
seen (p. 177) that this is the only method by which oxygen is
now made on a large scale.

The nitrogen which escapes from the top of the tower is led
into numerous small furnaces, filled with calcium carbide, and
heated to redness electrically. Here nitrogen is absorbed and
nitro-lime formed.

Nitro-lime, CaCNi, is a hard gray-black mass resembling com-
pact coke. As the formula shows, it is rich in nitrogen. It is
claimed that the nitrogen is rapidly oxidized to nitrates in the
soil and that nitro-lime is an excellent fertilizer, but agricultural
chemists do not seem to have reached an agreement on this impor-
tant point.

Definition

Nascent state. The state of an element at the instant of its libera-
Hon from a compound. The nascent state fa characterized by an
unusual chemical activity ^ which may be due to the fact that the
atoms have not yet had time to unite with each other to form mole-
cules.

CHAPTER XXIV

THE CARBONATES: BLEACHING POWDER, HYDROGEN

PEROXIDE, OZONE

409. Calcite. — ^When a broken piece of marble is ex-
amined it is seen to resemble loaf-sugar in structure. It
is composed of crowded crystals which have had no
space to develop. These are composed of a mineral called
caldte.

Under more favorable circumstances, calcite forms large,
colorless, transparent crystals which are found in various
forms, one of which is shown in Fig. 93. The same figure
iUustrates the power of the crystal to split light passing
through it into two rays, which take
different directions, so that objects, seen
through it appear double. This prop-
erty is called double refraction and is
utiUzed in optical apparatus.

410. The Metal of Caldte. — ^Whena , , .

u«x r 1 'J. • T_ ij • xu /I XI. Fig. 93.— A crystal of calcite.

bit of calcite is held m the name, the

orange color which appears proves that we are dealing with

a calcium compound (p. 262). The color is more intense if

the mineral is moistened beforehand with hydrochloric

acid.

Calcium is made from calcium chloride, CaCl2, which is obtained by
dissolving calcite in hydrochloric acid, evaporating, and dr3dng the resi-
due by heat. The calcium chloride is melted in a graphite crucible, which
forms the anode of the electric current. The cathode is an iron rod which
at first dips into the melt. Chlorine escapes at the anode, and calcium
separates and clings to the cathode. Later the iron rod, acting as
cathode, is gradually raised out of the liquid, so that the calcium itself
serves as cathode, and a lengthening rod of it is formed. Calcium is
now made very cheaply by this process, and no doubt important uses
will be found for it.

311

312 AN INDUCTIVE CHEMISTRY

411. Calcium — Some information concerning calcium is summarised
in the following table:

Symbol: Ca. Behavior towards oxygen: bums

Atomic weight: 40. brilliantly to calcium oxide CaO

Specific gravity: 1. 61 (very light (lime).

therefore). Behavior toward moist air: Rusts

Melthig-pohit: 760''. rapidly, must be kept in sealed
Chemical conduct: active but less bottles.

so than sodium.

When calcium is thrown into the water, hydrogen escapes, less r^idly
than from sodium and water, so that the experiment is attended with no
danger. The other product is calcium hydroxide, Ca(0H)2, which is
ordinary slaked lime,

Ca + 2H2O — >- Ca(0H)2 + H2

Calcium is not foimd free in nature, but its compoimds are so conmion
that it ranks fifth among the elements in abundance. The earth's
crust contains 3.5% of it, calculated as metal.

Barium and strontium resemble calcium closely. Barium and its
compoimds color the flame green, while the flame-color of strontium is
crimson. The nitrates of both metals are used in fire^works.

412. Chemical Nature of Caldte. — ^When calcite is strongly
heated, lime — ^which is calcium oxide, CaO — ^remains. If
an iron tube is used for the heating, and the gas which
escapes is passed into lime water, the liquid becomes cloudy,
showing that carbon dioxide is evolved.

Quantitative knowledge can be obtained by intensely heating a
weighed portion of powdered calcite in a crucible until it loses no
more in weight. The result is that 100 parts lose 44 parts of carbon
dioxide and leave 56 parts of Ume. The molecular weight of lime,
CaO, is 56. To find how many times CaO is to be taken in the for-
mula we divide the 56 parts by weight of lime by the molecular weight
of lime and find that there must be one CaO.

The 44 parts by weight of carbon dioxide, divided by its molecular
weight (CO2 = 44), shows that there is also one CO2 in the formula of the
mineral. The formula of calcite is therefore CaO, CO2 or CaCOz,
The chemical name of calcite is calcium carbonate.

The reason that the calculation of the formula of calcite is so simple
is that the molecular weight corresponding to CaCOa is just 100.

413. Calcium Carbonate. — Marble is often nearly puire
crystallized calcium carbonate, but it is frequently beauti-

THE CARBONATES 313

fully veined and colored by small quantities of impurities.
The specific gravity of marble is 2.7. Limestone is a com-
pact form, not visibly crystalline, and not so pure. It is
often colored blue, gray, or grayish black. Great quantities
of it are used in the blast furnace, in making cement and
lime, as a building-stone, and for road-making. ChaUc is
a soft limestone, composed of microscopic shells. Lime-
stone composed of large shells cemented together is common
in Florida. All limestones originated from animal remains,
but some have been so changed that all traces of their
origin are lost. Most shells are composed of calcium car-
bonate with organic matter. The pearl has the same com-
position.

414. Solubility of Calcium Carbonate. — Calcium car-
bonate is very slightly soluble in water (100 c.c. takes up
0.0013 gram), but water saturated with carbon dioxide dis-
solves about thirty times as much (100 c.c. takes up 0.0385
gram). Since all natural waters contain carbon dioxide,
which they get from the decaying organic matter of the soil,
they all dissolve calcium carbonate to some extent.

Water oozes through a bed of limestone until it comes to a water-
tight layer, along which it runs, at the same time dissolving the lime-
stone above. The result, in time, is a cavern, which may be many
miles in length. The water begins to drip from the roof, and as soon
as it appears there, some of its carbon dioxide escapes into the air.
This causes some of the dissolved calcium carbonate to separate, so
that a mass shaped like an icicle grows downward from the roof. This
is called a stalactite. Where the drip strikes the flcov, more carbon
dioxide escapes and a mound of calcium carbonate called a stalagmite
grows up. Often the two meet and form a column. Finally, the
cavern may be filled up again by growths of this kind.

415. Lime. — We have seen that when calcium carbonate is
heated it decomposes into lime and carbon dioxide:

CaCOa :^ CaO + CO2

Excepting the chemical changes of agriculture — which is
really a branch of applied chemistry — ^the "burning" of lime

314 AN INDUCTIVE CHEMISTRY

is the oldest of cfaemicat processes. It has been carried out,
in connection with the making of mortar, for fifty centuries.
It b a reversible cliange, limited at any fixed temperature
by the concentration of the carbon dioxide.

If marble ia heated in a sealed vessel to 5S0° it will decompoae until
the concentration c^ the carbon dioxide is great enough to produce a
presBure of 27 m. m. of mercury.
Then equilibrium sets in and there
is no further change, so long aa
temperature and preenure remain
the same.

If some of the carbon dioxide is

DOW removed, say by an air pump,

more marble will decompose, until

the concentration of carbon dioxide

which produces a pressure of 27

m. m. is restored. If the pump ia

Pio. M.-A rimpi. limekiln. ^^^ "» action, 80 that the pressure

is not allowed to reach 27 m. m., the

marble will all decompose and only Ume will remain. On the contrary,

if, at 550°, carbon dioxide is pumped into the vessel, so that its pressure

iskeptalwayBabove27m.m., all the lime will unite with carbon dioxide

and pure calcium carbonate wiU result.

At any other temperature, the same thing holds good, but the limit-
ing value of the pressure is different, being greater the higher the tem-
perature. In the cold, this value in practically tero, so that lime, when
exposed, unites with the carbon dioxide of the air and turns to calcium
carbonate. This is one reason why lime does not "keep."

The practical result is that, in "burning" lime, the carbon
dioxide must be removed as fast as it is formed ; otherwise the
change will stop as soon as the latter reaches the limiting
concentration.

A simple limekiln is shown in Fig. 94. The fire is at b,
below the hmestone (a). The heat decomposes the limestone,
and the constant current upward to the chimney carries off
the carbon dioidde.

There are two bad defects about this arangement. In the first place,
it is wasteful of fuel, for much heat is carried oft in the hot gases which
rush up the chimney. All the heat in the finished lime is lost also, for
it issimplycbilled by opening the furnace and then taken out. Another

THE CARBONATES 315

defect is that every time a batch of lime is finished, the whole process
must be stopped while the furnace is emptied and r&«harged. Both
these difficulties are overcome in the "ring furnace" which is widely used
for "burning" hme, bricks and cement. It is really a group of fumacee
(say fourteen) arranged in an oval around one chimney (Fig. 06). Each
furnace communicates with a common smoke-canal which leads to the
chimney, but the communicating pipe can be closed by a damper. The
fumacea can also be thrown into communication with each other
at wiU.

In the diagram, 13 and 14 are not in use. lliey are being emptied
and refilled. 1, 2, 3, 4 and 5 contain finished lime. This is being

Fia. 95.— Tbe ring funuiM.

cooled, but the beat is not wasted. Air enters at 1 and passes throi^
the others to 6, which is the only furnace in which there is a fiie. The
air to support this combustion is pre-healed. by the waste heat of the
finished lime in the first five furnaces.

Furnace number 6 is not connect«d with the chimney. The hot
gases are forced to pass throu^ 7, 8, 9, 10, 11 and 12 and thence to the
chimney. These compartments are filled with limestone, which be-
comes heated by the waste heat of the gases from 6.

After some hours, the fiie is transferred to 7 and 13, which is now
full of hmestone, is connected to the chimney instead of 12; the finished
and cooled lime is removed from 1, and the air enters at 2.

The fumace of Fig. 94 bums about 40 kilos of coal to produce 100
kilos of lime, but the fumace of Fig. 95 will produce Qie same result by
burning only 20 kilos of coal.

Ctdeium oxide, CaO {lime), is a white solid which does not
melt in the hottest flames, but, when strongly heated, gives

316 AN INDUCTIVE CHEMISTRY

out an intense light, called the ''lime light." It can be
melted and boiled at the temperature of the electric arc. It
is used in making mortar, in the manufacture of soda, am-
monia, bleaching powder and calcium carbide, in removing
hair from hides and in the manufactiu*e of glass.

416. Calcium Hydroxide. — ^When lime is sprinkled with
water, it becomes hot and crumbles to a white powder of
calcium hydroxide, ''slaked lime.''

CaO + H2O Z:^ Ca(OH)

The change is reversible, for if the slaked lime is heated,
steam escapes and lime remains. 100 c.c. cold water dis-
solves 0.14 gram of slaked lime. This solution is called
"lime water'' and is used in medicine. We have employed
it in the test for carbon dioxide, with which it forms a white
precipitate of calcium carbonate:

Ca(0H)2 + CO2 — ^ CaCO, + HjO.

Much carbon dioxide causes the precipitate to re-dissolve,
but it appears again when the gas is driven out by heat.

A small bit of calcium, thrown into water, liberates hydrogen and
forms a clear solution of calcium hydroxide. If the air from the lungs,
which contains over 4% of carbon dioxide, is bubbled through the liquid,
it becomes milky from separated calcium carbonate; but if one blows
through it for a long time, the latter dissolves and the liquid again be-
comes clear.

Mortar is a mixture of slaked lime and sand. At first it
"sets," or hardens somewhat, by simple drying. Then a slow
absorption of carbon dioxide from the air occurs, and the
calcium carbonate binds the grains of sand into a stony
mass. The sand tends to keep the mass porous and prevent
shrinkage. In the middle of thick walls, mortar may remain
soft for years.

Slaked lime stirred up with water is called "milk of lime."
Whitewash is simply milk of lime. When painted on a wall.

THE CARBONATES 317

it absorbs carbon dioxide and forms a coating of calcium car-
bonate.

Calcium hydroxide is the cheapest active base, and is used,
if it will answer the purpose, whenever a base is needed in
chemical industry.

417. Hard Water. — ^Water containing dissolved calcium
carbonate, or other calcium compounds, cannot be used for
washing with soap, because it forms no lather, but produces,
instead, a sticky film which is a calcium soap. The student
should have no difficulty in explaining why water, whose
hardness is due to calcium carbonate, can be softened by
boiling, while, if the hardness is due to calcimn sulphate,
boilmg has no effect.

Boiler scale is often due to dissolved calcium compounds,
which are left as a hard coating when the water evaporates
in the boiler. The student may also attempt to explain the
curious fact that water, whose hardness is due to calcium
carbonate held in solution by carbon dioxide, can be softened
by adding the proper quantity of lime.

418. Strontium Hydroxide. — Strontium hydroxide,
Sr(0H)2, resembles slaked lime, but is much more soluble in
water. It forms an insoluble compound with sugar, and is
much used in beet-sugar works in separating sugar from
liquids from which the sugar will not crystallize. The sugar
can be again liberated by treating the compound with carbon
dioxide.

419. Bleaching Powder. — In the manufacture of bleaching
powder a layer of slaked lime 10 cm. deep is spread on the
floor of a long, low chamber built of slabs of sandstone.
Chlorine is passed in through a clay tube and is absorbed by
the lime. The chamber is allowed to stand 12-24 hours, and
then the finished bleaching powder is shovelled out.

It is a white powder which smells of chlorine. It is un-
stable and deteriorates on being preserved, more rapidly
under the influence of light and warmth. There is still
doubt as to the chemical nature of bleaching powder. It ap-

318 AN INDUCTIVE CHEMISTRY

pears to contain a compound of the fonnula CaOClj, which
liberates chlorine with acids:

CaOCU + H2SO4 — ^ CaS04 + H2O + CI2.

Good bleaching powder yields 35% or more of its weight of
chlorine when treated with acids^ and all of its uses depend
upon this fact. It is sometimes used as a disinfectant, but
more often for bleaching cotton fabrics. The goods, sewed
end to end into strips which are sometimes 50 kilometers
long, are run by means of rolls into a dilute solution of bleach-
ing powder and then into dilute sulphuric or hydrochloric
acid, so that chlorine is set free in the fiber. Complex cleans-
ing operations precede and follow the actual bleaching.

420. Barium Oxide, Barium Peroxide. — Barium oxide, BaO,
is gray. When moistened it slakes to barium hydroxide, with
such energy that it becomes red-hot. Heated to redness in
a current of air, barium oxide absorbs oxygen and changes
to barium peroxide Ba02:

BaO + "7"^ BaOt

The change is reversible and the direction in which it proceeds de-
pends upon the concentration of the oxygen. Thus, if barium oxide
is heated in an iron tube to 700° and air led over it, barium peroxide is
produced. If now an air-pump is applied, the change proceeds from
right to left (see equation above), all the oxygen which has been ab-
sorbed escapes, and barium oxide is formed again. Oxygen was for-
merly made in this way.

Barium peroxide^ Ba02, is a grayish-white powder, used in
the manmfacture of hydrogen peroxide,

421. Hydrogen Peroxide. — ^When barium oxide is treated
with sulphuric acid, barium sulphate and water are formed:

BaO + H2SO4 --^ BaS04 + H2O

When barium peroxide interacts with concentrated sulphuric
acid, barium sulphate, water and oxygen are produced:

BaOa + H2SO4 — >- BaS04 + H2O + O
Finally, when barium peroxide interacts with cold dilvie

THE CARBONATES 319

sulphuric acid, no gas escapes. All of the oxygen unites with
the hydrogen, forming hydrogen peroxidey H2O2, which dis-
solves, and can be separated from the barium sulphate by
filtration:

BaOz + H2SO4 — ^ BaS04 + H2O2

Pure hydrogen peroxide is a thick liquid which smells like
nitric acid. It has a faint blue color which is only perceptible
in a thick layer. It is unstable, tending to separate into
oxygen and water with explosion:

H2O2 — ^ H2O + O

Commercial hydrogen peroxide is a 3 % solution in water. It
is used in bleaching wool, silk and feathers, and in surgery,
for washing wounds. The bleaching power is due to the
oxidation of the coloring matter by the loosely held oxygen.
It is often called "20-volume solution" because it yields
twenty times its volume of oxygen. This separation of the
hydrogen peroxide into water and oxygen takes place very
slowly but becomes very rapid in presence of certain catalysts,
like platinum powder, or manganese dioxide.

Most oil paints contain compounds of lead. The darken-
ing of paintings with age is partly due to the formation of
lead sulphide by the action of sulphur compounds which escape
into the air from the burning of coal and gas. Treatment
with hydrogen peroxide oxidizes the dark lead sulphide into
lead sulphate, which is white, and restores the original
colors:

PbS + 4 H2O2 — ^ PbS04 + 4 H2O

Hydrogen peroxide usually acts as an oxidizing agent. But
in some cases, it has the opposite effect. Thus when poured
over silver oxide, oxygen escapes and water and silver re-
main:

H2O2 + AgzO — >- H2O + 2Ag + O2

The atomic theory suggests that the cause of this curious
removal of oxygen from both substances is the tendency of

820 AN INDUCTIVE CHEMISTRY

the loosely held oxygen atom of the hydrogen peroxide to
unite with the loosely held oxygen atom of the silver oxide,
and form an oxygen molecule which, as we know, contains
two atoms.

422. Ozone. — The oxygen which escapes when barium
peroxide is treated with concentrated sulphuric acid has some
properties which ordinary oxygen does not possess. It has
a suffocating odor, slowly turns silver black, and gives a blue

Fig. 96. — ^Tube for the oonveraion of osone into oxygen.

color to starch-potassium iodide paper, showing that iodine
is Uberated. This peculiar form of oxygen is called ozone.

Ozone is made by the action of electric waves on oxygen.
The change is reversible, and when the concentration of the
ozone has reached a certain point (5-10%, according to tem-
perature and intensity of the electrical disturbance) no more
ozone is produced. By cooling the mixture of ozone and
oxygen with Uquid air, pure ozone may be obtained as a deep
blue black, explosive liquid which changes to a blue gas when
withdrawn from the cooling agent.

One fonn of apparatus for the production of ozone (Fig. 96) consists
of a double walled tube, coated inside and out with tin foil. Oxygen
circulates between the walls and, by connecting the two layers of tin
foil to the opposite poles of an induction coil, electric waves, like those
made use of in wireless telegraphy, are made to pass through the oxygen.

The weight of a liter of ozone is 2. 147 grams; hence 22.4
liters of it weigh 2.147 X 22.4 = 48 grams. Hence the
formula of ozone is O3. It is one and a half times as dense
as ordinary oxygen.

Ozone contains more energy than oxygen:'

3O2 — >- 208 = 68,000 Gal.

THE CARBONATES 321

Hence ozone is more active. It converts silver and mercury
into oxides, bleaches dye-stufifs, and attacks organic matter.
Rubber connections cannot be used in working with it.
When ozone is passed through a heated tube, it is completely
changed to oxygen. It is quite poisonous. The reputation
it has attained for health-giving qualities is entirely unde-
served. It is doubtful whether it is contained in the air.
Ozone is employed in the purification of water. When air,
charged with ozone, is allowed to bubble through the water,
the micro-organisms in the water are destroyed.

423. Carbonic Acid. — Since calcium is bivalent, the
formula of the acid corresponding to calcium carbonate,
CaCOs, would be H2CO8. It is called carbonic add. Al-
though the carbonates are numerous and familiar, the acid
has never been obtained. The solution of carbon dioxide
in water reddens litmus feebly and contains a little carbonic
acid:

H2O + CO2 — ^ H2CO3

We might expect to obtain carbonic acid by adding sul-
phuric acid to a carbonate:

CaCOs + H2SO4 — ^ CaS04 + H2CO3

It turns out, however, that the carbonic acid separates into
water and carbon dioxide, so that the real result is:

CaCOa + H2SO4 —>- CaS04 + H2O + CO,

Carbon dioxide, then, escapes, when a carbonate is treated
with an active add: and this serves as a test to distinguish
carbonates from other substances. Most of the carbonates
are "insoluble" in water. Sodium carbonate, ammonium
carbonate, and potassium carbonate are freely soluble.

424. Washing Soda. — ^The washing soda of the household
is a carbonate, as is shown by the brisk escape of carbon
dioxide, when an acid is poured over it. The application of
the flame test proves it to be a sodium compound. Water
can be detected in the crystals by heating them in a dry test
tube.

322 AN INDUCTIVE CHEMISTRY

From the formula of carbonic acid, H2C0t, and the fact that
sodium is univalenty we may predict that the formula of
sodium carbonate will be NatCOi. This is verified by
quantitative work. By heating a weighed portion of wash-
ing soda crystals, and noting the loss in weight, it can be
shown that they contain ten molecular weights of water, so
that the formula is NajCOi 10 H2O.

425. Sodium Carbonate. — ^The water of crystallization in
washing soda makes up nearly two-thirds of its weight and
plays no part in any of its uses. Hence it is prepared,
shipped and sold on a large scale as NasCOs, which is a white
powder. To make the crystals and ship them would triple
freight charges without yielding any advantage. The trade
name of Na2C08 is soda. In science, it is called sodium car-
bonate or, sometimes, anhydrous sodium carbonate (an-
hydrous meaning free from water).

426. Baking Soda. — Since carbonic acid contains two
hydrogen atoms, it ought to be possible to replace only one
by sodium, producing sodium hydrogen carhorude, NaHCOi.
This is the baking soda of the household. Following is a
comparison of some facts concemmg wa^huxg soda and bak-
ing soda:

Sodium Carbonate Sodium Hydrogen Carbonate

White powder White powder

Bitter nauseous ta^ Taste saline, not unpleasant.

n • Not poisonous, largely used in

A oisonous I** * *!• i«

medicine for indigestion, etc.

Melts undecomposed at red heat Decomposed by gentle heat.

100 c.c. water dissolve 20 grams 100 c.c. water dissolve 8 grams

(18^). (18^).

Used in soap-making, glass-mak- Used in making baking powder, in

ing, etc. cooking, and in medicine.

427. Applications. — Like other carbonates, baking soda liberates
carbon dioxide with acids. The chemical fire extinguisher contains a
bottle of sulphmic acid and a solution of baking soda, so arranged that
the two chemicals are mixed at the time of use. The pressure of the
carbon dioxide throws the stream, and the gas also plays a part in ex-
tinguishing the fire.

THE CARBONATES 323

In cooking, baking soda is often used with sour milk. The lactic acid
of the milk interacts with the baking soda, liberating carbon dioxide
which is caught by the sticky gluten of the dough, giving the finished
cake a light, porous structure. Baking powder contains, along with
baking soda, some substance which will act upon it after the manner of
an acid. "Cream of tartar" which is potassium hydrogen tartrate j
KHG4H4O6, is often used. Until the powder is wet, there is little action,
for the contact between the two substances is not close enough, but
when water is added they both dissolve and interact at once:

NaHCO, + KHC4H4O. — >- NaKC4H40. + H,0 + COa

"RocheUe salt"

Seidlitz powder is the same as baking powder, except that the materials
are mixed only at the moment of use.

428. Solvay Process. — ^When ammonium hydrogen car-
bonate is added to saturated rock-salt solution, baking soda
separates:

NH4 HCOs + NaCl :±^ NaHCOs + NH4CI (1)

ammoniimi hydro-
gen carbonate

Ammonium hydrogen carbonate results when ammonia,
water and carbon dioxide come together:

NHs + CO2 + H2O — ^ NH4HCO, (2)

Baking soda is easily changed by heat into sodium carbonate:

2 NaHCOs — ^ NajCO, + H2O + CO, (3)

These three chemical changes are the basis of the Sohay
process by which nearly two million tons of sodium carbonate
are made yearly.

A concentrated salt solution is saturated with ammonia gas in a
closed iron kettle and then transferred to an iron tower 20 meters high
containing perforated shelves. Here carbon dioxide, made by ''burn-
ing" limestone, is passed in at the bottom under a pressure of three
atmospheres. Equation (2) occurs first, then (1), and the baking soda
separates upon the perforated shelves, which also serve the purpose of
dividing the carbon dioxide into many little bubbles, to make it dissolve
more easily. The baking soda is then heated in revolving iron cylinders
to change it to sodium carbonate (3), the carbon dioxide being collected
and used again.

324 AN INDUCTIVE CHEMISTRY

The ammonium chloride solution, from the tower, is heated with
lime, to obtain ammonia:

2 NH4CI + CaO — >- CaCl, + HjO + 2 NH,

The anunonia is used again. The calcium chloride solution contains
the chlorine which entered the process as rock salt. Calcium chloride
can be obtained from this solution by evaporation and some of it is
recovered and sold, but it is difficult to market and is almost a waste
product. Thus most of the chlorine is wasted. Another defect of the
Solvay process is that the interaction in the tower is not complete. It
is limited by the concentration of the interacting substances, so that
only two-thirds of the salt enters the chemical change. The rest is
wasted, going into the rivers with the calcium chloride. In spite of
these bad features, the process is at present the cheapest way of mA-lcing
sodium carbonate, and it is worked on an enormous scale.

429. Potassium Carbonate. — Potassium carbonate, KsCOt,
is a white powder similar to sodium carbonate. It is con-
tained in wood-ashes, which were, for centuries, the sole
source of it. Hence it is called "potosA," from which the
name potassiiun has been derived. Nearly two thousand years
ago the German tribes made soap by boiling potash with fat.

Crude wool is rich in potassium compoimds, which pass
into the wash water produced when wool is scoured. Much
potassium carbonate is obtained by evaporating this water
to dryness alid heating the residue.

The sv{iar beet contains potassium compounds which dis-
solve with the sugar, when the beet is sUced and treated with
water, and remain dissolved after the sugar has been ex-
tracted from the solution (p. 317). The liquid is then evap-
orated to dryness and heated to redness. This is an im-
portant source of potassium carbonate.

These three sources are examples of the intimate con-
nection of potassium with animal and vegetable life. Potas-
sium carbonate is also made at Stassfurt, from the potassiiun
chloride which occurs there. It is a commercial product of
importance, though not on the great scale of sodium car-
bonate. It is used in glass-making (hard glass) and for the
preparation of other potassium compoimds.

THE CARBONATES

325

430. White Lead. — The important pigment white lead contains lead
carbonate and lead hydroxide. Its composition is indicated by the
formula, Pb(0H)2 2 PbCOs- It is made by the joint action of acetic
acid and carbon dioxide on lead. The acetic acid attacks the lead,
forming lead acetate, which is then converted into white lead by the
carbon dioxide.

In one process, finely divided lead, with acetic acid, is placed in a
huge cask which rotates on a horizontal axis, and carbon dioxide is
passed in.

In the old Dutch 'process^ which yields a product unsurpassed in
smoothness and covering power, a Uttle acetic acid is placed in the bot-
tom of an earthen pot, which is then filled with lead in folded thin sheets,
or in cast gratings. Numbers of such pots are stood in spent tan-bark,
which, in rotting, serves as a spurce of carbon dioxide. They are
covered with planks upon which are placed a second layer of tan-bark,
and another series of pots. This arrangement is repeated until the roof
of the shed is reached. In about three months the lead is almost com-
pletely changed to white lead.

Related Topics

431. Deliquescence. — When potassium carbonate is exposed
to air, it absorbs water, becomes damp, and finally forms a
solution. The name deliqicescence
is applied to this behavior, which
is also met with in many other
substances.

The student will at once suspect
that the concentration of the water
vapor in the air must have a great
influence upon deliquescence*
That this is the case is shown by
the fact that salt and sugar are
both deliquescent at the seashore,
on account of the increased con-
centration of the atmospheric
water vapor. Hence, at the sea-
shore, candy must be carefully protected from the air, and salt
requires occasional baking to expel the moisture.

It is easy to make air saturated with water vapor. We need
only to place a dish of water under a bell jar, Pig. 97. Its effect
upon substances may be studied by placing them under the jar
22

FiQ. 97. — Apparatus for investigating
deliquescence and efflorescence.

326 AN INDUCTIVE CHEMISTRY

in watch-glasses. In this apparatus, aU solids which are soluble
in water become ddiqitescent.

432. Efflorescence. — Washing soda, when preserved, slowly
loses water of crystallization and crumbles to a white powder.
This is called efflorescence. Like deliquescence, it depends upon
the concentration of the water vapor in contact with the sub-
stance. "Bluestone," CuSOi 5 HiO, retains its water in ordinary
air, but in very dry air it turns white and effloresces rapidly.
Such air is easily made by placing a dish of sulphuric acid under
a bell jar. Many crystals which are quite permanent in the
open air will be found to effloresce in this apparatus, for the
sulphuric acid takes up water vapor quickly, and keeps its con-
centration close to aero.

Most salts form several compounds with water. Thus
CUSO4 HsO, CuS043H,0 and CuS045H,0 are known. The
last is always obtained when copper sulphate is crystallized
from water solution in the usual way.

Some substances, when crystallized from alcohol solution,
form crystals containing definite proportions of alcohol. This
may be called alcohol of crystallization. Crystals containing
ether, chloroform, etc., have also been obtained.

Definitions

Hard water. Water containing dissolved calcium or
magnesium compounds, which prevent it from forming a lather
with soap.

Boiler scale. A hard incrustation which forms inside
boilers which are fed with water containing large quantities
of calcium or magnesium compounds.

Deliquescence. The absorption of water vapor from the
air, by a solid, forming a solution.

Efflorescence. The loss of water of crystallization, the crys-
tals crumbling to a powder.

CHAPTER XXV

MATCHES, PHOSPHORUS, SUPER-PHOSPHATE FERTILI-
ZERS, ARSENIC, ANTIMONY AND BISMUTH

433. Distillation of Match-heads with Steam. — A dozen
heads, broken from ordinary (not safety) matches, are placed
in the flask shown m Fig. 98. The flask, Fi, is half filled
with water and the liquid distilled.

If this is done in a dark room, a ring of clear greenish light
appears at iJ, where the steam condenses. After a time, little
colorless spheres of a waxy soUd collect mider the water in
F2, which receives the drippings from the condenser. If
the water is pom'ed
away, this soUd be-
gins to give off a
white smoke, and
is Imninous in the
dark.

This substance is
the element phos-
phorus, which

Fig. 98. — Extraction of phosphorus from match heads.

part of the mixture

of which the heads of matches are made. The symbol of

phosphorus is P, the formula P4, and the atomic weight 31.

434. Manufactare of Matches. — In the manufacture of matches, the
wooden splints are first dipped into melted paraflSn to make them take
fire more easily and then into a paste composed of:

Phosphorus, 4 to 7 per cent.

Lead dioxide (or some similar oxidizing agent), 50 per cent.

Warm water.

Dextrin, to bind the mass together (dextrin is the paste used for the

backs of stamps. It is made by gently heating starch).
The head is then covered with lacquer to exclude air.

435. Red Phosphorus. — If the experiment of § 433 is
tried with the heads of safety matches, no result is obtained,

327

328 AN INDUCTIVE CHEMISTRY

for safety matches contain no phosphorus. But when we
examine the box on which they are struck we find — cemented
to it by dextrin — a purplish-red layer, which contains a
second modification of phosphorus, called red phosphorus.
Red phosphorus is very different from the white phosphorus
contained in ordinary matches, as may be seen from the
following comparison:

While Phosphorus Red Phosphorus

Colorless Purplish red

Specific gravity 1.8 Specific gravity 2.25

Takes fire at 34"" Takes fire at 240""

Oxidizes rapidly in air at ordinary Oxidizes very slowly in air at or-

temperatures dinary temperatures

1 gram carbon disulphide dissolves Insoluble in carbon disulphide

nearly 10 grams

Ltmiinous in the dark Not luminous

Smells strongly of ozone Odorless

Intensely poisonous Not poisonous

Red phosphorus is made by heating white phosphorus to
260** for ten days in an iron kettle from which air is excluded.
The change evolves much heat:

P (white) — >■ P (red) + 27,000 cal.

Hence the white form contains more energy than the red,
and this is the cause of its greater activity.

The compounds made by combining the two forms with
the same element are identical. In spite of the universal
use of matches, the world's production of phosphorus is
small (1000 tons per year).

436. Safety Matches. — ^The heads of safety matches are made of
a mixture of sulphur or a combustible sulphide, like antimony sulphide,
with an oxidizing agent like potassium chlorate, KCIO3. The box car-
ries a layer of red phosphorus and powdered glass, cemented by dextrin.
When the head is drawn over this coating, a little phosphorus is torn off,
catches fire, and ignites the match. Safety matches can also be ignited
by drawing them rapidly over glass, or some other smooth surface.

437. Phosphorus Poisoning. — ^White phosphorus is a vio-
lent poison and, on account of the ease with which it may be

PHOSPHORUS 329

obtained, is frequently employed by criminals. Treatment
is difficult and complete recovery rare. The experiment of
§ 433 is frequently employed for the detection of white
phosphorus in cases of suspected poisoning.

There is also a chronic phosphorus poisoning which attacks
workmen in match-factories. The most characteristic symp-
tom is a decay of the bones of the lower jaw. The use of
white phosphorus, in making matches, is forbidden in many
European countries. Bums, which may easily result from
accidents in handling phosphorus, are quite dangerous and
difficult to heal.

438. Phosphorus Pentoxide. — Either form of phosphorus
bums readily, but with the white the combustion is more
violent. A glance at the thermochemical equation for the
change of white to red (p. 328) explains the reason. Red
and white phosphorus yield the same product. It can be
collected by placing a cold dry bottle over the burning sub-
stance. The glass becomes coated with a loose white
powder, which has been shown to have the composition P2O6
and is called phospfuyrus pentoxide.

439. Phosphoric Acid. — When phosphoms pentoxide is
thrown into water it dissolves, with a hissing sound, and the
liquid becomes warm. On standing or boiling, phosphoric
add J HsP04, is produced:

P2OB + 3 H2O — >- 2 H3PO4

Phosphoric acid, H8PO4, is a white solid which is very
soluble in water. It is an active acid.

440. The Calcium Salts of Phosphoric Acid. — ^When caU
dum filings are thrown into a solution of phosphoric acid,
there is immediate interaction, and, if sufficient calcium is
taken, a white insoluble powder of caldum phosphate results.
The student should recall the fact that calcium is bivalent:

3 Ca + 2 H8PO4 — >■ Ca8(P04)2 + 3 H2

That this is not the only calcium salt of phosphoric acid
becomes plain when a smaller quantity of calcium is used.

330

AN INDUCTIVE CHEMISTRY

The metal dissolves, but the liquid remains cUar. It contains
calcium hydrogen phosphatCy CaCHiPOi)^, which is freely
soluble in water. A solution of this substance, made by a
different method, is sold as a beverage under the name
"acid phosphate."

The relation between these two substances and phosphoric acid will
be made clear by the following formulas:

2 moleeuletphosphcwieaoid Calcium phosi^te

P0« — ^H P04=Cft

X >

P0« — ^H P04=Ca

Caleiiim hydrocen phcMphate

PO4 — ^H

Nca

P0« — H
\H

441. Minerals Containing Calcium Phosphate. — Calcium
phosphate, Ca8(P04)2, is an abundant mineral in the United

States and occurs in extensive beds in
Canada, where it is mined. It is called
apatite. Its crystals often have the hex-
agonal form shown in Fig. 99. They are
about as hard as glass and are often sea-
green. Crystals a foot or more in length
have been found.

Great deposits of impure amorphous
calciiun phosphate (phosphate rock) occur
in South Carolina, Tennessee and Florida,
more than a million tons a year being ob-
tained in the three states and used in the
manufacture of fertilizers. Enormous deposits exist also
in Idaho, Montana, Wyoming, and Utah.

White phosphorus is made by heating phosphate rock with
coke and sand in the electric furnace shown in Fig. 100. The
mixture is fed in at the hopper JET, the graphite electrodes enter
at GG and the slag is removed at C Phosphorus vapor escapes
through P and is condensed under water. The equation is:

Pig. 99. — A crys-
tal of apatite.

Ca, (P04)2 + 3 SiOj + 5 C

3 Ca SiO» + 5 CO + 2P

PHOSPHORUS 331

442. The Mineral Matter Required b; Plosts. — When a. plant is
burned, the organic matter is deetniyed, and tiie aah which remains is
derived from the ntineral matter, which the plant, in its growth, took
up from the Boil. In order, therefore, to support planUgrowth, the
soil must contain the

materiala which the plant H

requires. Important
among these necessary
constituents are:

1 Magnesium

2 Calcium

3 Iron

4 Sulphates
6 Potassium

6 Nitrates

7 Phosphates

The fijBt four are present
in such quantity in most
soils that there is no fear
of their exhaustion, even
if one crop aft^ another
is grown and romoved

from the land. But the pio. 100.— MmutaeWre of phosphorus.

last three are not so plenti-
ful and must be restored to the land to balance the constant drain by the
crops; otherwise exhaustion and barrenness will result. We have already
discussed potassium fertilization (p. 242) and nitrate fertilization (p. 306).
The great source of phosphates Cor fertilization is the phosphat« rock
of the Southern and Western United States,

Tte rock can be powdered and put directly upon the fields, but it is
very slow in its action, for calcium phosphate is "insoluble" in
water and is only gradually taken up by the roots. Calcium hydrogen
phosphate, Ca(HtPOi)i, however, is soluble and gives a quick result.
It is made on a large scale by treating the powdered phosphate rock
with sulphuric acid in a closed iron vessel:

Ca,(P04)i + 2 H,SO, >- Ca(H,P04)« + 2 CaSO*.

As a rule, no attempt is made to separate the calcium sulphate from
the product, for its effect is rather beneficial to the soil in most cases.
The mijrture of the two is sold as "superphosphate." It may be added
that both apatite and phosphate rock usually contain calcium fluoride,
CaFi, mixed with the calcium phosphate.

332 AN INDUCTIVE CHEMISTRY

The phosphorus compounds, which plants make from the phosphates
of the soil, are found mainly in the fruit and seeds. Cereals are rich
in them. From plants, phosphorus compounds find their way into the
animal body. About 60% of the bones and teeth is calcium phosphate.
Brain and nerve tissue contain large quantities of complex organic
phosphorus compounds.

443. Phosphine. — Phosphine, PHg, is a colorless, poison-
ous; combustible gas, which smells like rotten fish.

In a general way, with many exceptions, the phosphorus
compoimds are like those of nitrogen. Phosphine corre-
sponds to ammonia, NH3. This general relationship to ni-
trogen is also shown by the compounds of three other ele-
ments, arsenic, antimony and bismuth. Taken together, the
five elements are called the nitrogen group.

444* Arsenic (As = 75). — Arseno-pyrite, FeSAs, is a silver-
white, crystalline mineral, which occurs in many parts of the
United States. When it is heated in a test tube, a black
shining mirror of arsenic is formed in the cooler part of
the tube, while iron sulphide remains in the bottom:

FeSAs — >- FeS + As

Arsenic is made by heating arseno-pyrite in a horizontal
clay tube, into the mouth of which is fitted a roUed-up piece
of sheet iron, to receive and condense the arsenic vapor.
Arsenic is a brittle, crystalUne solid. When fresh, it has a
bright steel-gray luster, but it rapidly tarnishes and turns
blackish. It is easily converted into vapor, and its vapor
pressure reaches 760 m.m., and balances the pressure of the
air, before the melting-point is reached. Hence it vaporizes
without melting. When heated in vessels strong enough to with-
stand the pressure produced, it can be melted at about 500®.

About 0.5% of arsenic is added to the lead used in making shot.
The melted alloy is then poured into a perforated iron basin at the top
of the shot-tower. The drops fall 100-150 ft. into water. During the
descent they become round, just as a rain drop does, because the nat-
ural shape of a liquid, left to itself, is the sphere. The arsenic lowers
the melting point of the lead, making it more liquid and the shot more
nearly spherical. It also makes the finished shot harder.

ARSENIC

333

445. Arsenious Oxide. — ^When heated in the air, arsenic
bums to a white smoke of arsenious oxidcy AS4O6. The oxide
can also be obtained by heating areeno-pyrite in a current
of air and leading the gases through chambers and canals in
which the arsenious oxide deposits. It is obtained com-
mercially as a by-product in the roasting of silver, copper,
and nickel ores, many of which contain arsenic.

Arsenious oxide is a dense, white, crystalline powder,
which vaporizes without melting and is somewhat soluble in
water. It is a commercial product of considerable impor-
tance. It is added to melted glass to oxidize impurities and
remove discoloration. Compoimds made from it are widely
used by the farmer and orchardist in destroying fungi and
insect pests. It finds q

apphcation in taxi-
dermy and as a rat- ^^

poison. ^viv A

Arsenious oxide is v m I

very poisonous (fatal
dose, 0.2 gram or
less) and, since it is
easily obtained and
has a feeble taste, it
is frequently used by
criminals. The
poisons of the Borgias and the famous "Acqua Tofifana,''
with which more than six himdred persons were slain,
were prepared from it.

446. Arsine. — Arsine, AsHs, is a colorless gas with an of-
fensive smell. It is poisonous in the extreme. When led
through a tube heated to dull redness, it is decomposed and
the arsenic condenses to a blackish-gray shining mirror.
Marshes test for arsenic is based upon this behavior.

When a solution of arsenious oxide is added to a liquid in which hydro-
gen is being generated, the nascent hydrogen combines with the arsenic
and arsine escapes, mixed with hydrogen. For the lecture table, the

Fia. 101. — ^Marsh's test for anenic.

334 AN INDUCTIVE CHEMISTRY

hydrogen can be made in an ordinary gas bottle, from zinc and sulphuric
acid and lighted. When a drop or two of a solution of arsenious oxide
is poured in the funnel tube, the flame enlarges and becomes pale. If
a porcelain dish is held in it, black-gray spots of arsenic are deposited.
If the tube carrsdng the gas is heated, an arsenic mirror is obtained
(Fig. 101). This experiment is dangerous in unskilled hands.

In practice, zinc is objectionable, for it usually contains arsenic and
this might give rise to serious errors. The hydrogen is best made by the
electrolysis of dilute sulphuric acid in a vessel divided into two compart-
ments. Since hydrogen escapes at the cathode, the liquid to be tested
is introduced into the cathode-chamber, and the hydrogen led away
through a heated tube to see if an arsenic mirror results.

447. Antimony. — The chief ore of antimony (Sb = 120) is
the blackish-gray, crystalline mineral stibnite, which is
antimony trisidphide, SbjSs. When it is melted in a crucible
with scrap iron, antimony is formed:

SbsSs + 3 Fe — ^ 3 FeS + 2 Sb

Or, the stibnite can be roasted to antimony oxide and then
heated with coal, according to the general method of con-
verting sulphides into metal (p. 140). Stibine, SbHj,
resembles arsine and is formed in a similar way.

Antimony is crystalline, with a white metallic luster. It
does not rust, but bums to an oxide when heated. It is too
brittle to be used alone, but finds much application in harden-
ing softer metals, especially lead and tin. Compounds of
antimony are poisonous.

The bullets used in charging shrapnel shells are made of an alloy of
4 parts lead and 1 part antimony. Bullets of pure lead would be so soft
that they would be mashed together by the explosion, and those which
remained separate would be so changed in shape as not to carry far,
when the shell burst. Type metal is an allov of about 75% lead, 15%
antimony and 10% tin.

448. Bismuth. — Bismuth (Bi = 208) is found chiefly as
metal. It is extracted by taking advantage of its low melt-
ing point (270**). The ore is heated in an inclined iron
cylinder and the bismuth drains away from the other ma-
terials.

BISMUTH 335

Bismuth is brittle. It can be distinguished from other
metals by its pink luster, which is permanent, for bismuth
does not rust. It bums to an oxide when heated.

Some alloys containing bismuth melt at a lower tempera-
ture than any of the metals of which they consist. Thus
Wood's fusible metal contains:

4 parts bismuth (melting-point 270°)
2 parts lead (melting-point 327®)

1 part tin (melting-point 232°)

1 part cadmium (melting-point 320°)

The alloy melts at 60°. A spoon made of it would melt
in a cup of hot coflfee.

At bottom, the mechanism of fusible alloys is the same as the melting
of a mixture of ice and salt below 0°. When two solids can melt to
form a 8olutiony their mixture will melt at a lower temperature than
either alone.

Fusible allo3rs are used in automatic sprinklers. A pipe conveying
water has a plug of fusible metal, which melts in case of fire and releases
the water. Iron doors are held open by catches of fusible metal, which
being melted by heat, allow the doors to close and shut off the burning
portion of a building. ' Fuses in electric connections are made of fusible
alloys.

449. Compounds of Bismuth. — ^Bismuth is trivalent. The hydrox-
ide Bi(0H)3 is a very inactive base and hence hydrolysis (p. 289)
occurs when bismuth salts are dissolved in water:

BiCls + 3 H2O ^^ Bi(0H)3 + 3 HCl (1)

bismuth
chloride

Or, what is the same thing :

Bi -h 3 OH 1^^ Bi(0^8 (2)

bismuth
ion

Bismuth hydroxide is insoluble and forms a white precipitate. For
this reason, bismuth salts cannot be dissolved clear in water alone.
But if hydrochloric acid is added to the water in which bismuth chloride
is dissolved, the reaction is forced, by the increase in the concentration
of the acid, to proceed from right to left, and a clear solution results.

A compoimd which is at once an oxide and a nitrate of bismuth and
which has the formula BiONOs is largely used in medicine. It is
called bismuth sn^JlMiitrale,

336 AN INDUCTIVE CHEMISTRY

Related Topics

450. The Drying of Gases. — Phosphorus pentoxide absorbs
water energetically, and one of the most effective methods known
of drying a gas is to let it remain in contact with that substance.

No drying agent will completely absorb the water vapor from
a gas. When the concentration of the water vapor has fallen
to a certain limit, different for each substance, equilibrium re-
sults and no further drying takes place. The merit of phos-
phorus pentoxide is that the concentration of the water vapor in
equilibrium with it is very small, much smaller than with other
drying agents, like lime, calcium chloride or sulphuric acid.
For the rapid drying of large volumes of gases in practical
work, simple cooling is the cheapest method. The water vapor
is condensed or frozen out of the gas. In the manufacture of
iron, the blast of air for the blast furnace is frequently dried by
passing it over coils of pipe, which are cooled by brine from an ice
machine. The dry blast then goes to the blast stove and thence
to the furnace. A decided saving in fuel results.

We have already met some examples of the fact that carefully
dried gases are inactive chemically. A surprising instance is
that, when oxygen has been dried by phosphorus pentoxide,
white phosphorus can be melted (44°), or even boiled (290°) in
it, without igniting.

CHAPTER XXVI

THE SILICATES AND BORATES

451. Water Glass. — The chief constituent of sand is
quartz, Si02, often called silica. When clean white sand is
melted with sodium carbonate, carbon dioxide escapes and
sodium silicate remains:

NajCOa + SiOa — >- NaaSiOs + CO2

sodium
silicate

Sodium silicaie is a glassy mass, which is colorless when
pure, but is usually colored green by iron silicate. Long
boiling with water causes it to dissolve, and form a sirupy
liquid. Hence it is called water glass. This solution is the
form in which it is commonly sold. It is employed in fire-
proofing wood and cloth, as a cement, and as an addition to
cheap soaps.

452. Glass. — Calcium carbonate interacts with siHca at a
high temperature:

CaCOs + SiOj — ^ CaSiOs + CO2

calcium
silicate

When sodium carbonate and calcium carbonate are melted
with silica, the product consists of sodium silicate and
calcium silicate, which are imited to form a substance which
we may call sodium calcium silicaie. This is ordinary window
glass.

Glass is made by melting, in a large fire-clay pot, a mixture of (1)
powdered quartz, or clean white sand, with (2) some form of calcium car-
bonate, such as limestone or chalk, and (3) sodium carbonate. Sodium
ndphaie is often used instead of sodium carbonate. It forms sodium
silicate in a similar way and is cheaper.

The ph3rsical state of glass is just the same as that of the candy which
is made by melting sugar and cooling it, without letting it crystallize.
Such candy might almost be called ^'sugar glass." The liquid sugar, as

337

338 AN INDUCTIVE CHEMISTRY

it cools, becomes more and more viscous (stifiT), imtil, when cold, it is so
extremely viscous that we call it a solid. When this solid is heated, it
softens more and more until we can call it a liquid, but there is no defi-
nite temperature at which it melts. When kept, such candy often turns
to a mass of sugar crystals, which shows us that the glassy condition is
unstable.

Glass, as we have seen (p. 8), behaves in exactly the same way when
heated or cooled, and this softening makes glass-blowing possible. Like
the sugar candy, it is in an unstable state. When melted glass is cooled
too slowly, it sometimes crystallizes, which renders it opaque and
makes it necessary to remelt it. In very okl buildings, panes of glass
are often found which have become crystalline and lost their trans-
parency.

Lamp-chimne3r8, lenses and cut-glass objects are made of flint glass.
This is potassium lead silicate, made by melting sand with potassium
carbonate and lead oxide. It is denser than ordinary glass and re-
fracts light more strongly. The '^aste'' which is used to imitate gems
is flint glass rich in lead silicate, made by heating lead oxide and a little
potassium carbonate with sand.

The student will remember, from his laboratory work, that many
compounds of the metab dissolve in melted borax and color it. The
same colors are produced in glass by the same means. The green of
ordinary bottle glass is due to iron compoimds. Blve glass is colored
with cobalt compoimds and manganese compounds yield an amethyst
color. Imitations of colored gems, like the ruby, sapphire and emer-
ald, are made by coloring "paste" in this way.

Plale glass, for mirrors and shop windows, is made by pouring melted
glass on a cast iron table with a raised rim. The glowing glass is
smoothed at once by a heated iron roll.

The more silica a glass contains, the higher the temperature required
to soften it, and the better it resists the attack of chemicals. Ordinary
glass contains about 70%, and hard glass more, up to 80%. More than
80% of silica makes glass so resistant to heat that it is difficult to work
it on a large scale.

Pure quartz can be melted at a high temperature in a flame fed with
oxygen, and worked into crucibles, thermometer tubes, beakers, etc.
These articles are expensive. They will bear the full heat of the Bunsen
flame without softening, and they can be heated red-hot and plunged
into water without cracking.

453. Clay. — Just as a sulphate always consists of a metal
united to sulphur and oxygen, so a silicate consists of a metal
in union with silicon and oxygen, but, while the formulas of

THE SILICATES AND BORATES 339

the sulphates are simple, those of the silicates are very com-
plicated.

Clay is aluminium silicate^ Al2Si207, white when pure, but often
colored by iron compounds. Kneaded with water, it becomes plastic,
and can be shaped at will into objects, which become stone-hard when
dried and heated short of fusion. The manufacture of bricks and terra
cotta is based upon this behavior. These materials are porous, for the
clay shrinks in baking, and, since the external shape and size remain the
same, the mass acquires a spongy structure.

Porcelain is made by baking a mixture of pure, white clay with pow-
dered felspar. The temperature is pushed so high that the felspar melts
and partly fills the pores which would be left in the clay.

Portland cement is made by heating a mixture of clay and limestone
to a temperature at which the mass "sinters," but does not quite melt.
It is then finely powdered. Cement consists of calcium aluminium sili-
cate. When mixed with water, it sets to a stony mass, whose hardness
and strength slowly increase for years. In actual use, it is always
mixed with sand or broken stone. An excellent mixture is made by
adding to the cement an equal weight of sand.

Cement is taking the place of natural stone for many piuposes. More
than five million tons of it are now made yearly in the United States,
and the production is rapidly increasing.

4S4. Some Natural Silicates. — The silicates are very im-
portant rock-forming minerals. Limestone is the only
common rock which is not composed of them. Felspary
which is aluminium potassium silicate, is the most abundant.
It occurs in granite, and many other rocks, in crystals which
often have a pinkish pearly luster. Topaz, emerald and
aquamarine are examples of natural silicates used as gems.
The adds corresponding to the various silicates have never
been prepared.

Under the action of the weather, felspar slowly passes into
clay, giving up its potassium, which, being extracted in
soluble form, becomes available as plant-food. One of the
great chemical problems of the future is the preparation of a
potassium fertilizer from felspar, by making its potassium
soluble in some cheap and rapid way. Such a process would
at once make our country independent of the Stassfurt de-

340 AN INDUCTIVE CHEMISTRY

posits, for the amount of potassium locked up in the felspar
of our rocks is unlimited. A cubic yard of average granite
contains about 250 lbs. of potassium; a cubic yard of felspar
nearly 800 lbs.

455. Borates: Borax. — The familiar substance borax oc-
curs as a mineral in Tibet, whence it was first obtained.
That borax is a sodium compound is plain from its flame-
color. That it contains water appears in the same experi-
ment, for the borax froths and bubbles, when heated, be-
cause of the escaping water vapor. The acid of borax can
be detected by powdering a little, moistening it with sul-
phuric acid, and adding alcohol. When ignited the alcohol
bums with a green flame. This is the test for boric add.
Borax is sodium tetra-boraie. Its formula is NaiB4O7l0H2O.

Boron, the characteristic element of borax, is a greenish-brown pow-
der, insoluble in water. The addition of aluminium to melted steel
before casting has been mentioned. Boron is sometimes added, for
similar reasons, to copper, before casting. The boron removes any
oxygen which may have combined with the metal, and improves the
casting.

Borax is made from calcium borate, large deposits of which
are found in Nevada, California and BoUvia. When the
mineral is boiled with sodium carbonate solution, calcium
carbonate and borax are formed.

Borax is used for cleaning metal surfaces for soldering.
It dissolves and removes any oxide which may be on the
metal and allows the solder to come into perfect contact.
It is one constituent of the mixtures employed for glazing
pottery and enamelled iron-ware. Some soaps contain it.

456. Boric Acid. — Boricaddj H3BO3, canbemadeby adding
sulphuric acid to a solution of borax:

Na2B407 + H2SO4 + 5 H2O — ^ Na2S04 + 4 HsBO,

Boric acid forms white scaly crystals which feel greasy to the
touch. 100 c.c. of water dissolves 4 grams at 18**. The
solution is much used as an eye wash. Boric acid, when

THE SILICATES AND BORATES 341

added to meats or other foods, prevents the development of
the bacteria which produce decay. Hence it is employed as
a preservative, but the addition of chemicals to food-products
is a most objectionable practice.

Definitions

Silicate, A compound of a metal with silicon and oxygen.
Portland Cement, A calcium aluminium silicate which, when
' mixed with water, slowly hardens to a stony mass.

CHAPTER XXVII

CHROMIUM.— SOME IMPORTANT RARE ELEMENTS.—

RADIO-CHEMISTRY

457. Chromium. — The chief native compound of chrom-
ium (Cr = 52) is the black mineral chroma iron ore, FeCr204,
which comes mostly from Asiatic Turkey and from New
Caledonia, a French penal settlement in the Pacific, east of
Australia. Chrome iron ore is the raw material from which
the chromium compounds of commerce are obtained.

Chromic oxide, CrjOs, is called chrome green. It is a bright
green powder used for painting on china. When it is mixed
with aluminium filings and heated intensely at one point
by means of a fuse prepared for the purpose, there is an
energetic production of aluminium oxide and chromium:

CrjOs + 2 Al — ^ AI2OS + 2 Cr

Chromium is made on a large scale by this method. It is a hard,
bright, steel-gray metal, which melts at 2000°. It does not rust, but
passes into chromic oxide when heated. It dissolves in hydrochloric
acid, liberating hydrogen. Chromiiun has important applications in
the making of special steels. Armor plate is often made of steel con-
taining nickel and chromium. Tool-steeb frequently contain chro-
mium. "Invar** is steel containing 36% of nickel. It does not ex-
pand when heated, so that if the pendulum of a clock is made of invar
the clock will run in exactly the same way in hot weather as in cold.

458. Potassium Dichromate. — Potassium dichromaie,
K2Cr207,is made by heating chrome iron ore with potassium
carbonate, K2CO3, and lime. The object of the lime is to keep
the mass porous, which is necessary, because oxygen is ab-
sorbed in the chemical change.

Potassium dichromate forms orange-red crystals, soluble
in about eight times their weight of water. It is employed
in one type of electric battery, and in making chrome alum
(p. 287) and chrome yellow. Its most important use is in
tanning chrome leather, which is widely used, especially for
shoes.

342

CHROMIUM 343

459. Potassium Chromate. — When a solution of potassium
dichromate is mixed with potassium hydroxide, the orange
color gives place to yellow and, on evaporation, yellow crys-
tals of potassium chromate, K2Cr04, are deposited:

K2Cr207 + 2 KOH — ^ 2 K2Cr04 + H2O

A solution of potassium chromate, mixed with an acid,
turns orange and dichromate is formed:

2K2Cr04 + H2SO4 — >- K2SO4 + K2Cr207 + H2O

460. Chromium Trioxide. — When concentrated sulphuric
acid is added to a cold, saturated solution of potassium di-
chromate, scarlet needlesoichromiumtrioxide, CrOa, separate:

KaCraOy + H2SO4 — ^ K2SO4 + H2O + 2 CrOa

The Uquid is poured oflf from the crystals which are dried
upon a brick.

Chromium trioxide is a vigorous oxidizing agent. Warm
alcohol dropped upon the crystals takes fire. It is often
called chromic add, but of course it is not an acid, since it
contains no hydrogen. The true chromic acid which cor-
responds to K2Cr04 has the formula H2Cr04. It can be ob-
tained in rose-red crystals, by cooling a water solution of
chromium trioxide:

CrOa + H2O — ^ H2Cr04

It is very unstable, easily separating into chromium trioxide
and water.

461. The Chromates. — The chromates of the heavy met-
als are yellow or red, poisonous and often insoluble in water.
Lead chromate, PbCr04 (chrome yellow), is the most important.
It is obtained, as a bright yellow powder, by mixing solutions
of lead nitrate and potassium dichromate:

2Pb(N03)2 + KaCraOi + H2O — ^ 2PbCr04 + 2KNOs

+ 2 HNOa

It is largely used as a yellow pigment.

344 AN INDUCTIVE CHEMISTRY

Sodium dichramaley NatCrsO? 2 HtO, forms red crystals,
much more soluble in water than potassium dichromate.
It is cheaper than potassium dichromate and is displacing
the latter in conmierce. Sodium dichromate is made
by heating chrome iron ore with sodium carbonate and
lime.

462. Tungsten. — Tungsten is a metal which ahows much chemical
likeness to chromium. It is sold as a gray metallic powder, which can
be melted only in the electric furnace. It is used for the filament of the
tungsten lamp, which gives nearly three times as much light, for the
same current, as the carbon incandescent lamp. Five per cent of tung-
sten, added to steel, makes it very hard, and the hardness is retained
when the steel is heated and allowed to cool slowly, which is not the
case with ordinary steel. The ''self-hardening" tools, which can be
used, without softening, at such speeds that they become red hot, are
made of steel containing tungsten and chromium. Tungsten steels re-
tain their magnetism remarkably well, and are much used in the con-
struction of electrical measuring instruments.

463. Thorium and Cerium — ^the Welsbach Mantle. — Thorium and
cerium are two rare elements which have as yet found no application as
metals, but their oxides are important in connection with the Wdahach
manUe, which contains 09% of thorium oxide^ ThOs, and l%oi cerium
oxide, CeOs. Departure from these proportions in either direction im-
pairs the light, less cerium giving a feeble bluish-white light, and more, a
duD yellow.

MonazUe eand is the raw material of the mantle industry. It is
found in reddish brown grains in the beds of streams in North Carolina,
and in the beach-lands of the coast of Brazil. It is a phosphate of
various rare elements, of which thorium and cerium are the important
ones.

From it is prepared a solution of thorium nitrate containing a little
cerium nitrate, and into this is dipped the mantle, which is woven of high-
grade cotton or, sometimes, of ramie fiber or artificial silk. Heating
over the Bimsen flame bums out the cotton and leaves a residue of
thorium and cerium oxides, which retains the original gauzy texture.
The mantle is then hardened by a blowpipe flame which has a
high temperature. Dipping in collodion solution strengthens the
mantle, so that it can be transported without breakage. When in
use, the mantle is supported in a non-luminous Bunsen flame. All
the light comes from the glowing mantle. Per cubic foot of gas
consumed, the Welsbach mantle gives far more light than the naked
flame.

gf Uu WelabMh mantle upOD the pt

RADIO-CHEMISTRY 345

Related Topics

464. Radio-chemistry; an Experiment — In a room lighted
only by a dark-room lantern, a photographic plate is wrapped in
black paper. Outside the paper, on the film side, a Welsbach
mantle is flattened out by pressing it between the plate and a
piece of pasteboard. The arrangement is enclosed in a light-
tight box and left to itself two weeks. Then the plate is de-
veloped as usual. Fig. 102 shows the result.

The mantle has photographed itself upon the plate; therefore
it must have given off rays which affect the plate in the same
way as light. But these rays cannot be light, for light would
have been stopped by the black paper. Further work shows
that the radiation comes from the thorium of the mantle, for
thorium, and all of its compounds, produce the effect, while
cerium and its compounds are inactive.

465. Discovery of Radio-activity. — Our knowledge of radio-
activity started in 1896 with an experiment similar to the above,
made by Becquerel. He found that uranium compounds acted
upon the plate, through black paper in a dark room.

Uranium is a white metal resembling chromium, but less conmion.
Its compounds are mostly yeUow, and are used in coloring glass. Ura-
nium has the highest atomic weight of all the elements (U = 238). Its
most important mineral is pitch-blende, UsOg, usually very impure.

Fig. 103 shows the result of one of Becquerel's experiments.
There was an aluminium medal, with a head on it, between
the uranium compound and the photographic plate.

If the radio-activity of pitch-blende was entirely due to the
uranium, uranium itself would be more strongly radio-active
than pitch-blende. Madame Curie found, however, that some
specimens of pitch-blende which contained only 50% of ura-
nium were four times as active as uranium itself. She drew
the only possible conclusion; that pitch-blende must contain
traces of some new element, much more radio-active than
uranium, and she systematically worked up large quantities of
pitch-blende to search for this substance. The result of these
researches was the discovery of radium, which is more than a
million times as radio-active as uranium or thorium. When a
tube containing a strong radiiun preparation is simply drawn

346 AN INDUCTIVE CHEMISTRY

across a photographic plate, an impresaion is produced, which
appears whea the plate is developed (F^. 104).

466. Radium. — Radium (Ra = 226) is a white metal belong-
ing to the calcium group. It oxidises easily in the air and is
difficult to prepare. The actual work has been done with radium
chloride, RaCli, and radium bromide, RaBri, which are white
crystalline salts, soluble in
water. The best pitch-
blende contains only one
part of radium in five mil-
lion, so that, to obtain an
ounce of radium, more
than 150 tons of the min-
eral would have to be
worked up. The total
quantity of radium thus
far extracted, the world
over, is probably less than
an ounce.

467. Effectsof the Radi-
um Rays.^The radium
rays turn white phos-
phorus to red, convert
oxygen into ozone, cause
diamonds, zinc sulphide
and many other substances
Fia. 10s.— Eieotrifiad silk tiuaeL to shine In the dark, make

paper turn brown and
brittle, destroy the germinating power of seeds, and produce
severe bums on the hands of chemists who use them. No matter
how easy it may become to prepare radium, it will never be
kept and stored in quantity, for, as Professor Curie said, if a
man entered a room which contained a kilo of it, it would burn
all the skin off his body and kill him. The action of radium
upon the body has been applied, with some success, to the
treatment of cancer and of lupua (tuberculosis of the skin).

Radium compounds are constantly a little warmer than their
surroundings, that is, they give out heal. One gram of pure
radium would give out more than 100 cal. per hour. £ach hour

RADIO-CHEMISTRY 347

it would give out enough heat to raise its own weight of water
from the freezing- to the boiling-point.

Fig. 105 represents a silk tassel which has been charged with
electricity by friction with a sheet of rubber. It retains its
charge some time, for air is a non-conductor. But, when a
radium compound is brought near, the charge is instantly lost
{Fig. 106). The radium rays make air a conductor. Since meth-
ods of detecting conductivity in air are very perfect, this
furnishes ua with an inconceivably delicate test for radium or
any radio-active element.
Even the effect of a single
atom of radium can be
detected by its influence
upon the conducting
power of the air.

46S. Nature of the
Rays. — The puzzling
thing about the matter is
that all these effects of
the rays mean a constant
expenditure of energy.
The idea of a substance
radiating energy continu-
ously, without taking in
anything,isnewin science.
To explain the aource of
this energy is the problem.

The key to the solution
was supplied, when it was
shown that, unlike light,

the radium rays are Fio. lOS.— SilktaaHldiMhanedbyndiumnya.

material. The most Im-
portant rays, those which carry the greater part of the energy,
and produce most effect in making the air conduct electricity,
are atoms of helium, projected with the speed of 10,000 miles
a second. The speed of a rifle-bullet is about one-fourth of
a mile a second.

469. The Radium Emanation. — The constant formation of
helium from radium has been proved beyond doubt, and we

348 AN INDUCTIVE CHEMISTRY

must admit that the radium atoms are unstable, that they ex-
plode and shoot out helium atoms. What becomes of the ra-
dium atom after the helium atom has been pitched ofif? It can
no longer be radium. Since Ra » 226 and He -» 4 the atomic
weight of the other product must be 226 — 4 *» 222. It is a
dense gas, called the radium emanation.

He
Ra ^ Em

226 >- 222

The emanation has been condensed by cold to a colorless liq-
uid, which shines with a green light in the dark. It is intensely
radio-active. It has only been obtained in very small quantity.
Much of it would melt and vaporize any vessel in which it
was placed. Its atoms shoot out helium atoms and, in so
doing, it turns to a solid product of atomic weight 218, called
radium A.

Em RaA

222 >-218

Radium A shoots out helium atoms and changes into other sub-
stances which we have not space to discuss. It is possible that the
final product of the changes is lead. The total energy given out
by a gram of radium in passing through all these changes is about a
million times as great as can be obtained by the most energetic
known chemical chsCnge of one gram of material. However,
the change of radium takes place so slowly that 2500 years elapse
before it is half complete, and there is no way to accelerate
or retard it. In fact we have no control at all over radio-active
changes.

470. Origin of Radium. — How is it that there is any radium
left in the world? Why has not all of it long ago passed through
its cycle of changes and disappeared? The only possible an-
swer is that it must be continually produced afresh from some
element of higher atomic weight. Since radium is always
found in minerals containing uranium, there is strong reason to
think that uranium is its parent. This belief has been confirmed by

RADIO-CHEMISTRY

349

experiments, which show that uranium continually generates
radium.

This change of uranium into radium takes place in several
stages. We perceive, therefore, that the dream of the alche-
mists — the conversion of one element into another — has become
a fact. We must, however, remember that we have no control
over the process and can neither start it nor stop it.

CHAPTER XXVIII

SOME IMPORTANT (IMPOUNDS CONTAINING CARBON.

—COLLOIDAL SOLUTION

471. Nitroglycerine. — When alcohol is treated with nitric
acid, ethyl nitrate, a colorless explosive liquid, is formed, the
equation being similar to that for the neutralization of sodium
hydroxide by nitric acid:

NaOH + HNO5 — ^ NaNOs + H2O
CjHfiOH + HNO3 — ^ CaHfiNOs + H2O

alcohol ethyl nitrate

Compounds, Uke ethyl nitrate, in which the hydrogen of
an acid is replaced by radicals composed of carbon and hydro-
gen are called esters (p. 239).

Glycerine, C3H6(OH)8, is an alcohol containing three OH
groups. Its behavior toward nitric acid is similar to that of
a metal hydroxide containing three hydroxy 1 groups:

A1(0H)3 + 3 HNO3 — ^ A1(N03)3 + 3 H2O

aluminium aluminium

hydroxide nitrate

CaHsCOH), + 3HN0, — ^ CaHsCNO,), + 3 H,0
glycerine nitroglycerine

473. Manufacture and Properties. — Nitroglycerine is made by
slowly adding one pfiuii by weight of purified glycerine to a mixture of
2 parts of nitric with 3 parts of sulphuric acid. The object of the latter
is to concentrate the nitric acid by absorbing water from it. The mix-
ture of acids is contained in a lead-lined vessel and is kept cold by water
circulating in a coil of lead pipe, for, if the temperature goes above 25®,
explosions occur. A large tank containing cold water is provided, into
which the mixture can be run, in case the interaction becomes too
vigorous.

The nitroglycerine floats on the surface of the acid mixture. It is
removed and most carefully washed, with water and dilute sodimn car-
bonate solution, to remove traces of acid, which make it liable to spon-

350

COMPOUNDS CONTAINING CARBON 351

taneous explosion. 100 parts of glycerine yield 220 parts of nitro-
glycerine.

Nitroglycerine is a faint yellow, odoriess oil with a burning sweet
taste. It is poisonous and, in working with it, enough of its vapor is
inhaled to produce dizziness and headache. In small doses it is used in
medicine, as a powerful stimulant. It freezes at 12® and, when frozen,
is unfit for use as an explosive. Many disastrous explosions have re-
sulted from imskilKul attempts to "thaw out" nitroglycerine mixtures.

473. Explosion of Nitroglycerine. — ^As a result of shock, fric-
tion, or sudden heating, nitroglycerine explodes with great violence.
The chief explosion products are carbon dioxide, water and nitrogen-
329,000 calories are liberated by the explosion of a molecular weight
(227 grams).

As in the case of black gunpowder, the explosion is merely sudden
oxidation, but in gunpowder the oxygen and the substance to be
oxidized are in separate substances which are merely mixed — in
nitroglycerine they are in the same molecule. Hence, with nitroglyc-
erine, f/he explosion is more sudden and therefore more powerful.
Berthelot showed, by direct measurement, that the explosion traveled
along a tube filled with nitroglycerine, at the rate of 1300 meters a
second.

Nitroglycerine is so easily exploded by shock that it cannot be trans-
ported. This difficulty was formerly overcome by soaking it up in
porous earth, making a mixture called dynamite, which could be trans-
ported safely. This form of dynamite is now rarely used. Nitro-
glycerine is at present used chiefly in the form of "blasting gelatin"
(p. 352).

It is clear that nitroglycerine is simply the nitric add ester of glycerine.
Its relation to glycerine is similar to that of sodiimi nitrate, NaNOa, to
sodium hydroxide NaOH.

474. Nitrocellulose. — Cellulose, CeHioOs, interacts with a
mixture of nitric and sulphuric acids in the same way as
glycerine. The product is nitrocellulose.

The cellulose is used in the form of purified cotton fiber. It is allowed
to remain in the acid mixture half an hour, then drained in a centrif-
ugal machine and washed completely, first with cold and then with
boiling water. The cotton is xmchanged in appearance, but is harsher
to the touch. Lighted with a match it bums with extraordinary energy,
but without explosion. Friction between hard bodies, violent blows
or sudden heating cause it to explode. Unlike nitroglycerine, nitro-
cellulose is not a single, definite chemical compound. We may roughly
distinguish two varieties.

362 AN INDUCTIVE CHEMISTRY

475. Guncotton. — In guncoUon the interaction of the nitric acid with
the cellulose has been pushed as far as possiblei by using much sulphuric
acid in the acid mixture (to absorb the water), and by allowing the cot-
ton to remain in it till the action is complete. Guncotton contains up-
wards of 13% of nitrogen. Wet guncotton can be forced by hydraulic
pressure into a hard mass which, while moist, can be bored and sawed
like wood. This is employed for torpedoes (50-100 kilos for each)
and for submarine mines.

The surest way of exploding guncotton, or any high explosive, is to
detonate it. This means to explode, in contact with it, a small charge
of some other substance, and set off the guncotton sympathetically.
Mercuric fulminate is largely used for this purpose (p. 353). Gim-
cotton is rarely used in practical blasting, since blasting gelatin
(§ 478) is cheaper and more powerful.

476. Smokeless Powder. — ^A mixture of ether and alcohol does not
dissolve guncotton, but converts it into a plastic mass which, when
passed between rolls, comes out as a transparent sheet, not imlike horn.
This, cut into leaflets 1 m.m. square or thereabouts, is the smokeless
powder used by the United States, Germany, Russia, Japan, France and
Austria. The English powder (Cordite) contains 65% guncotton, 30%
nitroglycerine and 5% vaseline.

In addition to the absence of smoke, smokeless powder is much more
powerful than black powder. Its introduction has doubled the effective
range of the rifle, while the weight of the cartridge is only half that of
the old black powder cartridge — a great advantage, since it allows the
soldier to carry twice as many roimds *of ammunition. A disadvantage
is that the smokeless powder does not keep as well as the old black
powder. When preserved, the smokeless powder undergoes slow
changes which may lead to spontaneous explosion. Disastrous explo-
sions have occurred on warships from this cause.

477. Collodion. — ^In making collodion^ the action of the nitric acid
on the cotton fiber is not pushed to completion. The product resem-
bles guncotton in appearance but contains only 12 % of nitrogen and is
not so explosive. It dissolves in a mixture of alcohol (1 volume) and
ether (2 volumes) and the solution finds application in surgery and
photography.

Celluloid is made by rolling collodion at a gentle heat with half its
weight of camphor and a little alcohol. It is widely used for the back-
ing of photographic films, and as a substitute for ivory, whalebone and
amber.

478. Blasting Gelatin. — Nitroglycerine, warmed to 50®, dissolves
nearly one-tenth of its weight of collodion. On cooling, the mixture
solidifies to a transparent jelly called blasting gekUin, This is a more

COMPOUNDS CONTAINING CARBON 353

powerful explosive than either of its constituents; yet it can be trans-
ported safely, for it is not sensitive to shock or friction.

Pure blasting gelatin is too energetic for the use of miners and
quarrymen. Instead of dislodging the rock in large masses, it converts
much of it into powder. It is therefore mixed in practice with sub-
stances which moderate the intensity of the explosion. A common mix-
ture consists of:

65% blasting gelatin
25% sodium nitrate
10% flour
Another contains:

50% blasting gelatin
45% ammonium nitrate
5% flour

In these mixtures the flour is burned, at the moment of the explosion,
by the oxygen of the nitrate, but since this oxidation is much slower
than the detonation of the blasting gelatin, the explosion is less violent
and shattering. Such mixtures are called gelatin-dynamites. They
have almost entirely taken the place of the old earth-dynamite, and of
black powder.

479. Mercuric Fulminate. — Mercuric fvlmincUef HgC2N202, is widely
used as a detonator for high explosives. In making it, mercury is dis-
solved in an excess of moderately concentrated nitric acid at a gentle
heat, and alcohol (10 c.c. for each gram of mercury) is added. There is
a violent interaction, which is moderated by removing the flame. The
mercuric fulminate separates in heavy white crystals, which are well
washed with cold water.

The manufacture of mercuric fulminate is not dangerous in skilled
hands, but the filling of the dry substance into cartridges and caps is a
most perilous operation.

480. Esters of Acids Containing Carbon. — Although
acetic add, C2H4O2 (p. 201), contains four hydrogen atoms,
only one can be replaced in forming salts or esters. We may
call attention to this fact by writing the formula HC2H3O2.

When a mixture of alcohol and acetic acid is heated,
ethyl acetate is formed:

CjHfiOH + HC2H3O2 I^ C2H6C2H3O2 + H2O

ethyl
acetate

As the arrows indicate, the interaction is reversible: ethyl acetate in-
teracts with the water formed, reproducing alcohol and acetic acid,
so that equilibrium sets in when all four substances have reached a

354 AN INDUCTIVE CHEMISTRY

definite ooncentration. However, if sulphuric acid is added, to com-
bine with the water, the backward change is prevented and the for-
mation of the ethyl acetate goes on to completion.

Ethyl acetate is a colorless liquid, with a fragrant odor.
The higher acids in the same series (p. 204) form esters in a
similar way. Other alcohols can be used in place of ordinary
alcohol so that a large number of esters can be made.
They are chiefly liquids, having a pleasant, fruity odor.
The artificial fruit essences, like essence of bananas,
pears, pineapples, etc., are mixtures containing esters of
this series.

The esters must not be confused with the ethers, which are
the oxides of radicals like ethyl. Ordinary ether is eihyl
oxide (C2H6)20. It is a colorless liquid which evaporates
rapidly, when* exposed to the air. It is made by gently
heating alcohol with sulphuric acid. Ether is largely used
as an anaesthetic.

481. The Fats. — The animal and vegetable /ate are esters
of the higher acids of the acetic acid series with glycerine.
Thus butter is partly composed of the glycerine ester of
butyric acid, C4H8O2. Since only one hydrogen atom can be
replaced, we write it HC4H7O2.

The formation of this constituent of butter fat from glyc-
erine and butyric acid could be written:

C3H6(OH)3 + 3 HC4H7O2 ^^ C3H6(C4H702)8 + 3 H2O

glycerine butyric acid butjrrine

The chemical name of this part of butter fat is
biUyrine.

The equation is not to be taken as meaning that butyrine is actually
formed in this way from butyric acid and glycerine. It is intended
merely to show the chemical nature of butyrine.

Palmitic acidj C16H32O2 or HC16H31O2, and stearic acid,
C18H36O2 or HC18H35O2, both of which are white crystalline
solids, belong to the acetic series (p. 204). Their glycerine

COMPOUNDS CONTAINING CARBON 355

esters, called palmitine and steanne, are important con-
stituents of the fats:

C3H6(OH)3 + 3HCi6H3l02 — >- C3H6(Cl6H3i02)3 + 3 H2O

glycerine palmitic acid palmitine

C3H6(OH)8 + 3 HC18H35O2 ^ C3H6(Cl8H3602)8 + 3 H2O

glycerine stearic acid stearine

It matters very little whether these fat-formulas are remembered or
not, provided that the student gets a firm grasp of their meaning. He
should think about them somewhat in this way:

(1) Nitroglycerine, C3H6(N03) 3, is constituted like A1(N08) 8. The dif-
ference is that, instead of a trivalent metal atom Al, it contains a tri-
valent radical, CsHe.

(2) Stearine, C3H6(Ci8H3502) 3, is Uke C3H5(N03)3. The difference is
that, instead of a univalent radical, NO3, it contains the univalent
stearic acid radical, C18H36O2. Therefore the chain of ideas which
links the fats to simple salts, Uke sodium nitrate, NaN03, is about as
follows:

NaNOs >- A1(N03)3 >- C8H5(N03)3 >- C3H6(Cl8H3602)8

482. Soap. — When aluminium nitrate is treated with
sodium hydroxide solution, aluminium hydroxide and sodium
nitrate are produced:

A1(N08)8 + 3NaOH — ^ A1(0H)3 + 3 NaNOa

Nitroglycerine interacts, in the same way, with sodium hydrox-
ide: glycerine and sodium nitrate result:

C8H6(N03)3 + 3 NaOH — ^ C3H5(OH)3 + 3 NaNOi

When stearine is boiled with sodium hydroxide the chemical
change is precisely similar: glycerine and sodium stearate are
formed:

C3H6(Ci8H3602)3 + 3 NaOH— ^C3H5(OH)3 + 3 NaCi8H350,

stearine sodium stearate

Soap consists of sodium stearate, sodium palmitate and
sodium oleaie (which is the sodium salt of oleic a^ddj C18H34O2).

In soap-making, a fat, like tallow, palm oil or olive oil, is placed in a
large, open iron kettle, provided with a steam coil, and heated with a

356 AN INDUCTIVE CHEMISTRY

dilute solution of sodium hydroxide. When the fonnation of soap has
begun, more concentrated sodimn hydroxide solution is added, little
by little. The soap boiler judges when his fat is completely changed to
soap partly by the appearance, and partly by the fact that the bitter
taste of sodimn hydroxide remains, even after boiling the liquid, show-
ing that the sodium hydroxide is no longer being used up in acting upon
the fat.

When this point is reached, solid rock salt is added, which causes the
contents of the kettle to separate into two layers. The lower is a water
solution of glycerine, which, on account of its wide use in the explosive
industry, is a valuable product. The upper layer is a semi-liquid mass
of soap. It is run into iron forms, where it becomes solid, and is then
cut into bars by means of a steel wire, stretched in a frame.

This product may still contain half its weight of water. In making
the better grade of toilet-soaps, the crude soap is cut into shreds, dried,
kneaded with perfume (and sometimes coloring matter), and pressed
out in a long bar; which is cut into cakes, moulded and stamped.
Floating soaps are made light by forcing air through them, while they
are in a pasty condition.

Finished soap should not contain any sodium hydroxide, which is
known as "free alkali" and is injurious to the skin. This means that
the soap boiler must be careful not to use more sodimn hydroxide than
is needed to act upon the fat. The marked cleansinj; action of soap has
not yet received a satisfactory explanation.

When soap is used with ''hard water'' — ^that is water containing calcium
ions — ^no lather is formed, but calcimn soaps — ^that is, calcimn stearate,
palmitate^ etc. — are precipitated. Magnesium ions have a similar effect.

483. A Newer Method of Soap-making. — On accoimt of its use in the
explosive industry, the glycerine has now become as important as the
soap, and it is difficult to prepare pure glycerine from the soap-liquor.
For this reason another method of soap-making, by which pure glycerine
is readily obtained, is coming into extensive use.

Let us take stearine, which is the chief constituent of beef and of mutton-
fat, as an example. The fat is heated imder pressure with superheated
steam and a little lime. This converts it into glycerine and stearic acid :

C3H6(Cl8H3602)8 + 3 H2O >- C8H6(OH)8 + 3 Cl8H8«02

stearine glycerine stearic acid

The glycerine goes to the manufacturer of explosives. The stearic
acid is sold to the soap boiler, who converts it into its sodium salt (soap)
by boiling it with sodium carbonate solution:

2 Ci8H3«02 + Na2C03 — >- 2 NaCi8H3602 + COj + HjO

soap

THE ALKALOIDS

357

In addition to yielding pure glycerine, the method has the advantage
that the soap boiler can use sodium carbonate, which is much cheaper
than sodium hydroxide.

484. The Alkaloids. — The stimulating effects of tea and
cofifee are due to the presence of small quantities of a white
crystalline bitter solid, called caffeine. Cofifee, which has been
deprived of its caffeine, is now an article of conmierce and,
while its flavor is the same as that of ordinary cofifee, it has
no effect upon the nervous system.

Caffeine is, in small doses, a brain stimulant, and, in large
doses, a poison. It colors red litmus blue and interacts with
acids, forming salts, and since, in these properties, it resembles
the bases or alkalies, it is called an alkaloid.

There are many other alkaloids. They occur mainly in
plants. Most of them are poisonous. Some of them, Uke
morphine and cocaine, are invaluable medicines, but, when
abused, become habit-forming drugs and produce the most

Alkaloid

Atropine
Caffeine

Cocaine

Morphine
Nicotine

Quinine

Strychnine

FormtUa

C17H21NO1
C8H10N4O,

C17H21NO4

Ci7HwN0t
C10H14N,

CioHmNiO,

C«HmN,Oj

Source

■j Nightshade ?•
Tea and coffee

Coca-leaves

C Seed capsules ^
< of the opium >•

( poppy. )

Tobacco

Bark of cin-
chona and
other tropical
^ trees

J Seeds of nux
I vomica

Effect

Dilates pupil. Used
in eye-surgery.

Brain stimulant.

Local anaesthetic.
Used in eye-
surgery, etc.

Narcotic

Used in treatment
of fevers.

Powerful nerve and
muscular stimu-
lant.

358 AN INDUCTIVE CHEMISTRY

destructive results. Most alkaloids are only slightly soluble
in water and therefore their chlorides or sulphates are used
in medicine.

The list on page 357 contains a few of the more important
alkaloids. All those mentioned are white crystalline solids,
except nicotine, which is a colorless, oily liquid. The
formidas should not be memorized.

All alkaloids contain carbon, nitrogen and hydrogen.
Most of them contain oxygen also.

485. The Albumins or Proteins. — White of egg consists
chiefly of a compoimd which, when extracted in pure condi-
tion, is found to contain carbon, hydrogen, oxygen, nitrogen
and sulphur (the student can remember these five elements
by the syllable CHONS, made from their symbols). This
compound is usually called albumin and is a type of a most
important class of compoimds called the proteins, which are
always present in animal and plant substance.

All of the proteins contain thefive elements just mentioned,
and many of them also contain iron, phosphorus and other
elements. They are a necessary constituent of human food;
it is impossible to sustain life on a diet which does not con-
tain them. Among foods rich in them are:

Meat 15% protein

Poultry 13-16% protein

Fish 12-16% protein

Eggs 13% protein

Cheese 27% protein

Beans or peas (undried) 7% protein

Chocolate 13% protein

Hardly any of the proteins can be obtained in crjrstals;
hence it is difficult to purify them. They are very unstable;
in fact it is their readiness to undergo chemical changes which
fits them to serve as the raw material of the complex series of
chemical changes which occur in digestion. For these rea-
sons, the investigation of the nature of these bodies is a
most difficult problem, and it is only recently that, owing

EMIL FISCHEK
B. Oeimaii)', tS4T.

COLLOIDAL SOLUTION 359

to the brilliant work of Emil Fischer ^ we have obtained a
clear notion of their chemical structure.

486. Glue and Gelatin. — Certain portions of slaughtered cattle,
like the hoofs, ears and tails, are unfit either for food or for tanning.
Such refuse goes to the manufacturer of gltie who boils it with water in
steam-heated kettles. The skin-substance swells up, loses its structure
and gradually dissolves. The clear solution, freed from imdissolved
matter, is evaporated until it contains 25% of protein, and is poured
out upon a table covered with glass plates, which are cooled by water
from below. Here it rapidly solidifies to a transparent plate, which
is cut up and dried.

Grelatin is a pure glue, made from clean sheep-skin by the same
method.

Related Topics

487. Colloids and Crystalloids. — Like almost all proteins,
gelatin never forms crystals. Thomas Graham in 1861 was the
first to point out that we must carefully distinguish crystalline
from non-crystalline matter.

(1) Substances which formed crystals he called crystalloids.
Such are salt, sugar, and almost all the substances studied in the
preceding chapters.

(2) Substances which could not be obtained in crystals he
called colloids, which means glue-like bodies. Starch, cellulose,
almost all proteins, rubber and the gums
are colloids. Our knowledge of the colloids
is just in its beginning, but that they are
important is plain from the great industries
which are based upon them. A few of the ^^^ ^^j — Diaiyzer
industries which operate almost entirely

with colloids are paper-making, photography, the various
branches of the great textile industry, rubber manufacture,
tanning, starch manufacture and agriculture. The bodies of
animals and plants consist chiefly of colloids.

488. Colloidal Solution. — One peculiarity of colloids we have
already noted. Unlike crystals, they have no melting-point,
but soften gradually as they approach the liquid state. An-
other can be investigated by the apparatus of Fig. 107, which
is due to Graham. It is called a dialyzer and is merely a shallow
glass cylinder with a bladder, or other animal membrane, tied over

360

AN INDUCTIVE CHEMISTRY

Fio. 108.— Makinc » colloidal
solution of gold.

one end. When a solution of table-salt is poured in this vessel —
which is then placed with the bladder dipping into a little water in
a dish — ^the salt passes through the membrane and divides itself
between the outer and inner liquids.

Other crystalloids act like the salt — the membrane allows
them to pass through it. But when a solution of gelatin, too

weak to "set," is placed in the
inner vessel, no gelatin penetrates
the membrane and the water in
the outer vessel remains free
from it. Other colloids dissolved
in water behave like gelatin —
the membrane stops them com-
pletely.

We have seen that a solution

of a crystalloid in water boils

above 100** and freezes below 0**.

But our solution of gelatin boils at 100"^ and freezes at 0"^.

TAe boiling- and freezing-points of a colloidal aolvHon are the same

as those of the pure liquid,

489. The Colloidal Solution of Gold. — Recent work shows
that most "insoluble'' substances can be obtained in colloidal
solution if the proper conditions are supplied. Gold is an ex-
ample. Two rods of pure gold are connected with a d3mamo
circuit of 220 volts and brought close together under the surface
of distilled water (Fig. 108). The arc bums between the rods,
with a clattering noise, and a purple color rises from them and
fills the liquid.

The gold has been vaporized by the heat and the vapor is
condensed so suddenly by the cold water that there is no chance
for the molecules to collect into crystals: particles of gold con-
taining only a few molecules are formed and these produce a
colloidal solution in the water.

The purple liquid is clear, for the particles in it are too small
to be detected even with the microscope. They can be examined,
however, by the arrangement shown in Fig. 109, which is a
simple form of the ultra-microscope.

In a darkened room a powerful beam of light is thrown by a
mirror, /S, against a lens, L, which focuses it, into the gold-solu-

COLLOIDAL SOLUTION

361

tion contained in a little glass trough 6. The liquid is examined
with a good microscope. It is then seen to be filled with multi-
tudes of red, yellow and green particles, all of which are in
rapid, ceaseless, zig-zag motion. This motion does not stop,
even if the preparation is preserved for years. It is the heat
motion of the molecules^ which becomes evident because the par-
ticles of gold are so extremely small. Except for the colors, the
appearance is similar to that of a swarm of gnats, flying about
in a sunbeam. The motion not only resembles in general

Fig. 109.— a simple ultra-microfloope.

character that required by the kinetic theory, but actual
measurement shows that the speed of a particle and the average
distance it moves in a straight line, before starting off in a new
direction, are just about equal to the values obtained by cal-
culation from the mathematics of the kinetic theory. Silver,
platinum, copper and other metals can be obtained in colloidal
solution by the same method.

Fig. 110 shows the motion of gold particles of various sizes.
Both particles and path are 3000 times the actual linear dimen-
sions. The smaller the particle the more vigorous the motion,
as we approach the dimensions of the single molecule. Still
smaller are the molecules of gases, which move with about the
speed of rifle-bullets, and beyond them, in the realm of the

362 AN INDUCTIVE CHEMISTRY

infinitely little, is the electron, a particle which weighs 2000 ^^

much as the hydrogen atom, and is shot out of some radio-
active atoms with nearly the velocity of light. This appears
to be the fundamental unit, of which the atoms of all the ele>
ments are built up.

An electric current is a swarm of electrons in motion. About a
billion billion electrons pass each second through the carbon fila-
ment of an ordinary sixteen candle-power incandescent lamp.

Pio. 110.— Motion op Pabticlbs in Colloidal Solutions of Qold.

1. Gold particle of 0.00001 millimeter diameter.

2. Gold particle of 0.0005 millimeter diameter.

3. Gold particle of 0.001 millimeter diameter.

4. Gold particle of 0.004 millimeter diameter (motionless).

Magnified 1:3000 ^.

Thus, the difference between electricity and matter is that, in
electricity, the electrons are independent of each other; in matter,
the electrons are grouped, in an orderly way, to form the atoms of
the elements.

Definitions.

Ethers. The oxides of the hydrocarbon radicals. Ordinary
ether is ethyl oxide (C2H5)20.

Soap. Sodium palmitate, sodium stearate, sodium oleate, or a
mixture containing them.

Alkaloids. A class of plant products which are alkaUne to indi-
cators, form salts with acids and have a powerful action upon the
body.

Colloids. Substances which, like glue, cannot be obtained in
crystals.

COLLOIDAL SOLUTION 363

Crystalloids, Substances which usually exist in crystallized
conditions. Crystalloids can be obtained in colloidal condition,
but they are then in an unstable state and tend to crystaUize.

Colloidal Solvtion. The dispersion of a solid through a liquid,
in particles so small that each can contain only a few molecules;
an intermediate stage between suspension and solution. Both
colloids and crystalloids can be obtained in colloidal solution.

Electrons, The minute particles which make up the atoms of the
elements; the fundamental units of which matter and electricity
consist.

CHAPTER XXIX

THE CLASSIFICATION OF THE ELEMENTS.— THE PERI-
ODIC LAW

490. Nature olf the Problem. — In our study of chemical
compounds, we have found it necessary to daasify them —
that is, to divide them into groups in such a way that the
members of each group exhibit a general similarity in prop-
erties. Examples of such groups are acids, bases, salts,
esters, hydrocarbons and carbohydrates. We have now to
inquire what progress has been made in classifying the
elements.

We might begin by dividing the elements into solids,
liquids and gases. More than sixty of the elements are solids.
Only two, mercury and bromine, are liquids. Ten —
chlorine, fluorine, hydrogen, nitrogen, oxygen and the five
inert elements of the argon group — are gases.

Such a grouping would be of little service. The solids
include such widely different elements as sodium, carbon
and sulphiu*. Mercury and bromine show no chemical
similarity. Among the gases, we find elements — ^fluorine,
nitrogen and argon for instance — ^which exhibit such striking
differences of chemical behavior that it is absurd to attempt
to include them in the same group.

491. Metals and Non-metals. — ^A better classification of
the elements is into mstals and non-metals. Fifteen elements
are non-metals. These are: arsenic, boron, bromine, carbon,
chlorine, fluorine, hydrogen, iodine, nitrogen, oxygen,
phosphorus, selenium, silicon, sulphur and tellurium.

The inert elements of the argon group are non-metals, so
far as their physical properties are concerned. Since they
have no chemical properties, they form a class by themselves.
They are: argon, helium, krypton, neon and xenon. All of
the remaining elements, sixty or more, are metals.

364

CLASSIFICATION OF ELEMENTS 365

492. Physical Properties of Metals and Non-metals. —

When polished, the metals have a peculiar luster called the
metallic luster. This is due to the fact that they are very
opaque and hence, when polished, reflect regularly most of
the Ught which falls upon them.

The metals are tenacious. An iron wire, suspended verti-
cally, would reach a length of two miles and a half, before
it would break of its own weight. Steel is much more
tenacious than iron. A steel rod, 1 square centimeter in
cross section, requires a force amounting to the weight of
8000 kilograms to pull it asunder. The other metals are
inferior to iron and steel in tenacity, but those which are in
common use, like copper, zinc and tin, are far more tenacious
than the non-metals.

The metals are more or less ductile: that is, they can be
drawn hxto wire. One gram of gold can be drawn mto a
wire three thousand meters in length.

The metals are more or less malleable: that is, they can be
beaten out imder the hammer. Gold, which is by far the
most ductile of the metals, is also the most malleable. It
can be beaten into leaf less than 0.00001 centimeter in
thickness.

The solid nortrmetals are hriUU. - When struck with a
hammer they are crushed to pieces. They cannot be beaten
into foil nor drawn into wire. The metals are good con-
ductors of heat and of the electric current, silver standing
first in both respects. The non-metals are non-
conductors or very poor conductors, both of heat and of
the current.

Several exceptions to the above statements must be noted.
Antim^ony, which is commonly regarded as a metal, is very
brittle. Sodium, potassium and some other metals have
little tenacity. Iodine, graphite and silicon resemble the
metals in luster. Graphite is a fairly good conductor of the
current and, on this accoimt, is widely us6d for electrodes in
the electro-chemical industries.

366 AN INDUCTIVE CHEMISTRY

493. Chemical Properties of Metals and Non-metals. —
The hydroxides of the metals are bases. Sodium hydroxide
and potassium hydroxide are familiar examples. Many of
the metallic hydroxides are insoluble in water — ^those of
nickel, copper and iron for instance — ^and these cannot, of
course, affect the color of red litmus, but they can still be
considered as bases in the sense that they interact readily
with acids, forming salts. The metals, therefore, are base-
forming elements.

On the contrary, the non-metals show a tendency to enter
into the composition of adds. Hydrochloric, nitric and sul-
phuric acids are striking instances of acids composed of non-
metallic elements. Acids containing metals are known, but
they are unstable and unimportant. The non-metals,
therefore, are acid-forming elements.

Another interesting distinction is mthehydrogen compound
of the two classes. The hydrogen compounds of the non-
metals are rather stable and are mainly gases. Water, which
is a liquid easily converted into a gas, is the chief exception.

Very few of the metals combine with hydrogen. The
metal-hydrogen compounds which have been obtained are
solids and are very unstable, being easily decomposed, at a
slightly elevated temperature, into metal and hydrogen.

The most striking property of the atoms of the metals is
their tendency to form positive ions in water solutions.
WTien a salt of a metal is dissolved and ionized, the metal
atom forms the positive ion and the rest of the molecule the
negative. For example see table on opposite page.

Positive ions composed of single atoms of non-m^etalsy other
than hydrogen^ are unknown. It follows from this that salts
in which the hydrogen of acids is replaced by single atoms
of non-metals are impossible. Such an impossible compound
would be, for example, chlorine nitrate, CINO3. The
chlorine atom cannot take up a positive charge, and the com-
pound cannot exist.

All this may be summed up briefly in the statement that

CLASSIFICATION OF ELEMENTS

367

hydrogen and the metals are electro-positive, while the non-
metals are electro-negative. An important practical result is
that the metals are always deposited at the negative pole
during electrolysis.

494. Classification of the Metals. — During the middle ages
the metals were divided into the ^^base metals ^'^ which lost

Substance

Molecule

Positive Ions

Negative Ions

Sodium chloride
Sodium nitrate
Sodium sulphate
Sodium acetate

NaCl

NaNOs

NafiS04

NaC2H302

+
Na

+
2Na

+
Na

CI
NO3
SO4
C2H3O2

their luster and were converted into oxides when heated, and
the ^^nohle metals,*^ which were not changed into oxides when
heated and were said to "stand the fire test." Copper is
an example of the first class and gold of the second.

It is clear that the difference is simply one of chemical
activity. Gold is an inert element. It has little tendency
to combine with other elements, and its compounds, when
formed, are easily decomposed. Hence, when gold is heated
in the air, no combination with oxygen occurs. On the con-
trary, gold oxide, AU2O8, is easily decomposed by heat.
Copper is far more active than gold, so that, when heated, it
combines with oxygen, and the compound, once formed, is
not easily decomposed by heat.

The noble or "precious" metals, therefore, are simply those
whose chemical activity, compared with that of the other
metals, is slight. Since metals of this class occur only in
small quantities in the earth's crust, they are costly.

495. Light and Heavy Metals. — A rough but serviceable
classification is into light and heavy metals. The light metals

368 AN INDUCTIVE CHEMISTRY

include those, like sodium, potassium and calcium, whose
specific gravity is less than 5. The heavy metals are those,
like copper, lead, tin and iron, whose specific gravity is
greater than 5. This latter class includes almost all the
metals in common use.

The light metals are active. They bum energetically when
heated. Many of them are rapidly converted by water into
their hydroxides, hydrogen escaping. Their tenacity is very
much less than that of the heavy metals. These properties
unfit them for constructive work. The tieavy metais com-
bine with oxygen and interact with water much less rapidly
than the light metals. They are more ductile, malleable
and tenacious. Some of them are constructive materials of
enormous importance.

Owing to their chemical activity, the light metals are some-
what difficult to separate from their compoimds. Their
preparation in the free state could not be effected until the
methods of oiu* science had developed sufficiently to accom-
plish the task. They were obtained in fairly pure condition
during the 19th century. Many of the heavy metals, es-
pecially the more abimdant ones, were known to the ancients.

Aluminium occupies an exceptional position. Its specific
gravity (2.6) places it with the light metals. In agreement
with this stands the fact that it is difficult to obtain from its
compounds. But, when once separated, aluminium is Uttle
acted on by air and water, and can be applied to many pur-
poses for which the other light metals are entirely unsuit-
able. This pecuUar behavior is due to the fact that
an invisible film of aluminium oxide forms on the sur-
face. This film acts Hke a varnish, and protects the metal
beneath.

496. Natural Families of Elements. — We have already dis-
cussed the chlorine group, often called the halogens^ as an
example of a natural family of elements. Another good
example of a natural family is the sodium group, consisting
of the following elements:

CLASSIFICATION OF ELEMENTS

369

Ndme

Symbol

Atomic
Weight

Spec. Gravity

Mdting^Point

Lithium

Sodium

Potassium

Rubidium

Caesium

T.i

133

0.6

0.95

0.86

1.5

1.9

186**

96^

63**

38^

27^

Like sodium, the other members of the group are nearly
silver-white metals, soft enough to be cut with a knife. A
glance at the right-hand column shows that, as the atomic
weights rise from Li = 7 to Cs = 133, the melting-points
fall. Caesium is a liquid on a warm summer day. In
specific gravity, a gradual increase can be traced from
lithium to caesium, though the regularity is broken by potas-
sium, which is a trifle less dense than sodium.

The chemical activity increases regularly from lithium to
caesium. One instance of this is the interaction of the five
metals with water. They all liberate hydrogen rapidly,
formmg their hydroxides, thus:

Li + H2O -^- LiOH + H

In the case of lithium, the temperature does not rise high
enough either to melt the metal or to ignite the hydrogen.
Sodium melts, but the hydrogen does not usually catch fire.
With potassium, ignition of the hydrogen always occurs.
Rubidium, and especially caesium, explode violently with
water.

Under the halogens (p. 258) we discussed a similar case of
gradual variation in chemical activity with varying atomic
weights. Such instances force upon us the question as to
whether the properties of an element do not depend upon its
atomic weight in somewhat the same way as the area of a
circle depends upon its radius. In mathematical language,
the question is whether the properties of an element are
functions of its atomic weight.

370 AN INDUCTIVE CHEMISTRY

497. The BlectroiL — ^The subject may be looked at from another
point of view. The facts of radio-activity, and other facts whose de-
tailed discussion belongs to Phjrsics, indicate clearly that the actual ma-
terial of which the atoms consist is the same in idl the elements. The
eUctran is a particle which seems to weigh about 71^ as much as a
hydrogen atom. The atoms of the elements are groups of electrons.
All of the atoms of the same element contain the same number of
electrons, but the numbers in the atoms of different elements are dif-
ferent and are proportional to the atomic weights. For instance, it
must take about twice as many electrons to make an atom of nitrogen
(N » 14) as to make an atom of lithium (Li » 7). Since the different
properties of the elements can only be due to the different number and
arrangement of the electrons, we are led to expect a very real connection
between the properties of an element and its atomic weight.

498. The Periodic Law. — ^The way to investigate this
connection is to arrange the elements in the order of increasing
atomic weights and ascertain how their properties vary as
the atomic weights increase. Omitting hydrogen, here are
the first sixteen elements:

01 2 34667

Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine
He =4 LI =7 Be=9 B = ll C=12 N = 14 O = 16 P = 19

Neon Sodium Magnesium Aluminium Silioon Phoephonu Sulphur Chlorine
Ne = 20 Na = 23 Mg = 24 Al = 27 81 = 28.5 P =: 31 8 = 32 CI = 35.5

Helimn is one of the chemically inactive gases of the argon
group, lithium is a metal very similar to sodium, fluorine is
a gas which resembles chlorine very closely and is the most
active of all the non-metals. The elements between the
two are intermediate in character: any element is less me-
tallic than the element to the left of it. Thus in passing
from lithium to the right there is a gradual loss of metallic
properties, which finally, when we arrive at fluorine, is
complete.

Now the next element in order is neon (Ne = 20), one of
the inert gases of the argon group. There is no gradual
transition from fluorine to neon. We pass at once from the
most active non-metal to a completely inactive element.
After neon comes sodium (Na ^ 23), one of the most posi-
tive of the metals. There can be no doubt that sodium
belongs in the same group as lithium, for the two resemble

THE PERIODIC LAW 371

each other in a remarkable way. This is true also of the
elements which follow sodium in the second Une; each is like
the one above it in the first Une. Magnesium is similar to
beryllium, aluminium to boron, and so on. This similarity
is greater at the ends than in the middle of the table. Sodium
is more similar to lithium, and chlorine to fluorine, than
aluminium is to boron, or silicon to carbon. Yet the similar-
ity between these middle elements is great enough to show
that they belong together.

499. The "Law of Octaves." — Thus these two sets of
eight elements each exhibit a relationship like that of two
octaves in music:

1st octave CDEFGABC

2d octave cdefgabc

In fact, when this remarkable arrangement of the elements
was first brought forward, it was called the "law of octaves"
for that reason. The properties of the elements change with
increasing atomic weight, and the change is a periodic one
— ^that is, similar elements occur again and again as the
atomic weight increases, very much as the hours repeat
themselves m different days, or the seasons m different years.
This periodic change in properties, with increasing atomic
weight, is the root-idea of the periodic law, and, if all the
elements behaved like the first sixteen, the whole matter
would be very simple. We should arrange the elements, in
the order of increasing atomic weights, in horizontal lines, each
containing eight elements, and those elements falling in the
same vertical Hne would belong together and would show
similarity in properties. We shall see at once that the real
state of things is more compUcated than this.

500. Long and Short Periods. — ^The set of elements from
helium to fluorine we call the first short period, and that from
neon to chlorine the second short period. The next eighteen
elements in the order of increasing atomic weights are the
following.

372

AN INDUCTIVE CHEMISTRY

§00.

This set begins, as we should expect it to, with an inactive
gas. Then follows a metal (potassium) . whose similarity to
sodium and lithium is very great. Farther along in the first
line, we discover that we have here a different ^

arrangement from that of the short periods.
Chromium is not very similar to oxygen and
sulphiu*, in whose vertical group it falls, for it
is much more metallic in character ; while the
similarity between manganese, on the one
hand, and fluorine and chlorine on the other,
is remote, manganese being, in most of its
chemical conduct, a metal. Yet, though in
both cases the elements differ from the cor-
responding ones of the short periods, there
are still some striking points of similarity
which justify us in classing chromium with
oxygen and sulphiu*, and manganese with
fluorine and chlorine. One important differ-
ence between this arrangement and that of
the short periods is, then, that at the element
numbered 7 — manganese in this case — the
metallic properties have partially but by
no means completely disappeared. Further,
the next metal, iron, is by no means; an
inert gas like argon, as it should be if it stood
at the beginning of a new short period. The
three elements of the column numbered 8 — '

p ■ © ■

iron, cobalt, and nickel — resemble each other
strongly. Copper is not nearly as positive a
metal as potassium. In the last seven
elements, from copper to bromine (Br =80),
there is a gradual and complete disappea^-^
ance of the metallic characteristics. Bromine
is an immistakable non-metal, and belongs
in the same group as fluorine and chlorine.
This set of eighteen elements is called the

§5 as

)00

•S g a

THE PERIODIC LAW 373

first long period^ and the general plan on which a long
period is built is this: First stands one of the inert gases
of the argon group, and second one of the active metals of
the sodium group. In the following six elements the
metallic qualities diminish, but do not completely disappear,
so that the element numbered 7, manganese, for instance,
shows mixed metallic and non-metallic characters. The
position of the three following elements is peculiar. Their
atomic weights lie near together (compare the atomic
weights of iron, cobalt, and nickel), and they resemble each
other strongly. Finally, through the remaining seven
elements the metalUc properties gradually and completely
vanish, so that the last member of the long period is, in all
respects, a non-metal.

501. Grouping of the Elements According to the Periodic
Law. — ^The complete arrangement of the elements according
totheperiodiclawisgiveDinthetableonpage 374. The vertical
columns are called groups, and the student will be prepared
to find that elements in the same group resemble each other.
It is convenient to divide each group mto two sub-groups, and
the resemblance between members of the same sub-group is
especially close. Thus, in group 1, the members of the sodium
groupy lithium, sodium, potassium, rubidium, and caesium,
resemble each other far more than they resemble the ele-
ments of the copper groupy copper, silver, and gold. The
elements of group O are all inert gases, those of groups 1 and
2 are all metals, and so are all those of group 3 except boron.
With this exception, the non-metals are all contained in
groups 4, 5, 6 and 7, and the most active non-metals stand
at the top for, in a sub-group composed of non-metals, the
non-metallic properties decrease with increase of atomic
weight. This is well shown by the fact that no non-metal is
known having a higher atomic weight than that of tellurimn
(Te = 127.5). In a sub-group of metals, the reverse is us-
ually true — ^the higher the atomic weight the more marked

the metallic properties.
25

374

AN INDUCTIVE CHEMISTRY

t»

Oft
1^

Oft

S 3^

«0 Pi

O O

"* P.

I |o

"(I! Or?

»c

Oft

is"

hiQQ

o «
OQ

5z;

0«

■^f

.-^

•5CLi

<§

^ at

a> a

9«
eg

Oft"

»o2

GO M

■s

"8
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cogs
080

C0(

Oft

CI
CI

THE PERIODIC LAW 376

The sodium group contains those elements which, from
the chemical point of view, manifest metallic properties in
the • greatest perfection. The most positive metal of these,
and, in fact, the most active metal known, is caesium
(Cs = 133), which has the highest atomic weight in the group.

502. Prediction of Elements. — The student will notice
at once that there are many gaps in the table. A gap arises
when we are forced to leave a vacant space for the sake of
preserving the arrangement. Thus, in the second long
period, after molybdenum (Mo = 96) in the sixth group, the
next known element m order of mcreasmg atomic weight, is
ruthenium (Ru = 102). Now the whole chemical character
of this element shows that it belongs in the eighth group,
and not under manganese. Further, if we simply proceeded
in order, placing ruthenium under manganese, not only
ruthenium itself but every following element would be thrown
out of place, and the whole latter portion of the table would
be disarranged. Therefore we leave a vacant space and pre-
serve the arrangement, believing that the place under man-
ganese belongs to some unknown element, which has an
atomic weight of about 100. Thirty years ago, when the
table was first published, gaps were more numerous. The
Russian chemist Mendelejeffy the originator of the periodic
law, gave it as his opinion that the vacant spaces would be
filled by the discovery of new elements. In several cases
he predicted in detail the properties of these elements and
their principal compounds, from the place which they ought
to occupy in the table. These predictions were verified,
the properties of the newly discovered elements agreeing
with Mendelejeff's statements with wonderful closeness —
a striking proof that the periodic classification is a real law
,of nature and not a mere artificial arrangement.

503. Method of Prediction. — ^The method employed by Mendelejeff
in predicting the properties of undiscovered elements will be made clear
by an imaginary example. Suppose that sodium was unknown. There
would then be a vacant space in the periodic table in group 1, between

376 AN INDUCTIVE CHEMISTRY

lithium and potassium. In the horizontal series, the gap would occur
in the 2nd short period, between neon and magnesium.

The atomic weight of the imknown element should be i^proximately
the mean of its two vertical neighbors:

Li = 7
K = 39

2) 46

23
or, the mean of its two horizontal neighbors:

Ne = 20
Mg - 24

2) 44

Since, in this family, the melting-point falls with increasing atomic
weight, the melting-point of the imknown element will be somewhere be-
tween that of lithium (186^) and that of potassium (63^). We
predict roughly that the imknown element would melt at a temperature
not far from 100®.

Its physical and chemical properties would resemble those of lithium
and potassium. It would be soft enough to be cut with a knife, would
bum readily when heated, and would communicate a marked color to
the flame of the Bunsen burner. It would lose its luster instantly in
moist air and interact rapidly with water, liberating hydrogen and form-
ing a hydroxide, which would be an active base.

The working out of the further details of the prediction may be left
as an exercise to the student. It can be extended to the prediction of
the properties not only of the unknown element, but also of its com-
pounds.

504. Defects of the Periodic Arrangement. — The periodic
arrangement is far from perfect. The upper portion of the
table, as far down as lanthanum (La = 139), is substantially
complete. There is only one vacancy, which belongs to an
undiscovered metal in group 7, whose atomic weight will be
about 100. Its horizontal neighbors are molybdenum (Mo)
and ruthenium (Ru), and it will resemble manganese.

But after we leave lanthanum, the vacant places become
so numerous that the latter portion of the table is quite*

THE PERIODIC LAW 377

fragmentary. Of course, there is not the slightest reason to
believe that all of the elements have been discovered and
investigated. It is possible that all these gaps will be filled
by the results of future research.

Another difficulty is that hydrogen finds no place in the
table. The student can find no better way of testing his
knowledge of the table than to attempt to fit hydrogen into
it. He will find it impossible to place it in any of the eight
groups. The entire omission of an element of such impor-
tance, and of such unique chemical properties, is a serious
defect in the table.

A further complication is that, in three cases, an element
has a slightly smaller atomic weight than the one which pre-
cedes it in the table. The pairs of elements in which this
curious contradiction occurs are the following:

Argon (Ar = 40) — Potassixim (K = 39)
Cobalt (Co = 59) — Nickel (Ni = 58.7)
TeUurixim (Te = 127.5) —Iodine (I = 127)

The properties of these elements are such that it is im-
possible to follow the order of increasing atomic weights
without putting each element of the pair in a group in which
it would be very much out of place. Thus, if we followed the
order of increasing atomic weights we should have to place
potassium with the inert gases and argon with the sodium
metals, which would be a most imreasonable classification.

The periodic law is not a complete and perfected
classification of the elements. It is still in its formative
stage. In pointing out profitable subjects for research, and
in fixing the true values of the atomic weights, it has been of
great value to our science. The future will probably
modify it in important details, but the fundamental fact that
the properties of the elements are periodic functions of their
atomic weights will remain.

CHAPTER XXX

CHEMICAL CALCULATIONS

Note to Teachers. — ^The time allotted to chemistry in most schools
will not permit the teacher to give all of the following problems, or even
half of them, to his class. The author has attempted to supply a
sufficient number of problems, of various degrees of difficulty, so that
each teacher can choose those which suit the special needs of his
students. Some of the problems are too difficult for many beginners.
There are, however, in every class, students with a special aptitude for
this work, who solve simple problems without much effort, and who
lose interest in the subject imless something worthy of their ability
is provided.

Note to Students. — ^Use the approximate atomic weights in solving
all problems.

505. Calculation of the Effect of Temperature, Pressure,
and Water Vapor on the Volumes of Gases. — 1. Tempera-
ture. — The absoliUe temperature is the temperature measured
from 273° below 0** C. Thus, the absolute temperature of
10° is 273 + 10 = 283°.

The absolute temperature of -10° is 273-10 = 263°.

Problem

I. Calculate the absolute temperature corresponding to the following
centigrade temperatures:

a. 13°. h. 274°. c. —50°. d. —273°.

The volume of a mxiss of gas is directly proportional to its
absolute temperature.

XT 1 /-kij 1 \y New abs. temperatiu*e
New volume = Old volume X-— -i — - —

^Old abs. temperature

In words, this means if we know the volume of a mass of
gas at some known temperature, we can calculate its volume
at some other temperature by multiplying the old volume by
the new temperature, and dividing by the old temperature,
both temperatures being absolute.

378

CHEMICAL CALCULATIONS 379

Never make the error of using ordinary centigrade tem-
peratures, instead of absolute temperatures. It is easy to see
that this leads directly to absurd results. For instance: I
have a liter of gas at 0° C. What will its volume become at
273° C?

Here, if we use ordinary centigrade degrees, the volume
becomes

273

that is, the volume is infinite — which is absurd. But if
we employ absolute degrees, the volume is

546
1 X -g = 2 hters;

which is the correct result.

Problems

3. What volume will a liter of air at 0° C. occupy at 100® C?

3. 5 1. of oxygen at 0** C. occupy what volume (o) at 10** C? (6) at
-10** C?

4. 25 jc.c, of nitrogen at 15** C. will measure what at the standard
temperature, 0® C?

5. I have 500 c.c. of hydrogen at 13® C. What will the volume be-
come at 65® C?

6. 600 c.c. of oxygen at 28® C. will measure what at -14® C?

7. 500 1. of air at 20® C. will occupy what volume at 80® C?

8. A liter of steam at 100® C. will occupy what volume at 120® C?

9. 67 1. of air are heated from -30® C. to 60® C? What is the new
volume?

Since the volume of a mass of gas varies with the tempera-
ture, it is always necessary, in measuring gases, to know the
temperature of the gas measured. And it is clear that the
expression "1 liter of oxygen" has no meaning unless some
particular temperature is either stated or understood. Now,
in order to avoid the necessity of continually stating the
temperature, it is' extremely convenient to assume some

380 AN INDUCTIVE CHEMISTRY

temperature as a standard point which is to be understood
unless some other temperature is stated. The standard
temperature universally agreed upon is 0* C — the melting^
point of ice. Thus, when a writer speaks of "1 liter of oxy-
gen'' without stating the temperature under which the gas
was measured, we know that 0* C. is meant.

The student should grasp the fact that every problem like
those just solved is supposed to deal with a certain mass
of gas which is not added to or subtracted from during
the process of heating or cooling. Clearly, if temperature
and pressure remain the same, the volume must be directly
proportional to the weight of the gas. Thus, 1 gram of
hydrogen at standard temperature and pressure occupies a
volume of 11 . 2 liters. Evidently, 2 grams of hydrogen must
measmre 22.4 liters under the same conditions, and so on.
But, in all problems of this sort, the quantity of gas is sup-
posed to remain the same.

2. Pressure. — The volume of a mass of gas is inversely pro-
portional to the pressure upon it. Usually the two pressures
are stated in millimeters of mercury.*

Old Pressure

New Volume = Old Volmne X

New Pressure

That is, if the volume of a mass of gas is given at some
pressure and it is required to calculate its volume at some
other pressure, we must multiply the old volume by the old
pressure and divide by the new pressure.

Problems

10. 10 1. of gas at a pressure of 743 m.m. will occupy what volume
at 720 m.m.?

11. 18.5 c.c. of nitrogen are measured under a pressure of 745 m.m.
What will the volume be at 760 m.m.?

12. A liter of oxygen is measured at 760 m.m. What will it measure
at 748 m.m.?

13. 100 c.c. of air at 760 m.m. (1 atmosphere) will occupy what volume
under 20 atmospheres?

CHEMICAL CALCULATIONS 381

14. What pressure is required to compress 500 c.c. of carbon dioxide
at 728 m.m. to a volume of 400 c.c?

15. What must the pressure be made in order to allow the 500 c.c.
of gas of the preceding problem to expand to 850 c.c?

In order not to be compelled to state continually the pres-
sure, in speaking of the volumes of gases, and in order to
be able to compare gas volumes, measured at different
temperatures, with each other, 760 m.m. of m£rcury is agreed
upon ds the standard pressure, which is understood when no
pressure is stated. This pressure is called 1 atmosphere, be-
cause the pressure of the air does not vary widely from that
amoimt.

Since, as we have seen, 0** is the standard temperature, the
expression "standard conditions" means C and 760 m.m.
Thus, when a writer speaks of 1 liter of oxygen (or of any
volume of any gas) without mentioning either temperature
or pressure, we understand at once that the gas is supposed
to exist at 0°, and under a pressure of 760 m.m. The abbre-
viation STP is often employed for standard temperature
and pressure.

3. When temperature and pressure both vary, we have simply
to correct for both, by the methods already studied. This
can be done in two separate calculations, but it is easier and
better to unite both corrections in one operation. The
volume of a gas is directly proportional to the absolute
temperature, and inversely proportional to the pressure.

Therefore

XT TT 1 rMj xr 1 w New abs. temp. v. Old Pressure

New Volume = Old Volume X 7:7-; — ; X r;^ ;;^

Old abs. temp. New Pressure

In words, this means that in order to calculate the new
volume of a gas at some new temperature and pressure, we
must multiply the old volume by the new absolute temperature
and the old pressure, and divide it by the old absolute tempera^
ture and the new pressure.

Such calculations can be rapidly, easily and correctly
made by the use of logarithms, and this is true of chemical

382 AN INDUCTIVE CHEMISTRY

calculations generally. A table of logarithms is given for
this purpose, and its use will save about half the time and
labor of chemical calculations, and will greatly reduce the
number of errors in the numerical work.

Problems

z6. 100 c.c. of oxygen at 15^ C. and 740 m jn. will occupy what volume
at standard conditions?

273 740
New Volimie - 100 X r— X -— - 92.3 c.c.

288 760

1. .

Note. — ^The student will find that his chief difficulty in solving
problems like this and the following ones is in determining which
temperature and pressure to put in the numerator and which in the
denominator. It will pay to make it a rule to inspect the fractions with
great care before working out the calculation. Errors can be detected
by the exercise of a little conunon sense. For instance, in the preceding
problem the gas is to be cooled from 15^ C. to 0^ C. This will reduce

273 288

its volume. Hence, the temperature-fraction must be -— , not — .

2oo 273

Also, the pressure is to be raised from 740 to 760, and this also will

740 760

reduce the volume. Hence, the pressure-fraction must be -— , not - — .

760 740

17. Supposing the initial temperature in the preceding problem to be
-15° C. instead of 15° C, what would be the new volimie? The other
figures remain the same.

18. What volume will 48 c.c. of nitrogen at standard conditions
occupy at 18° C. and 733 m.m.?

19. 25 1. of a gas at standard conditions are cooled to -10° C, and
the pressure reduced to 723 m.m. What is the new volume?

30. 310 c.c. of hydrogen at 10° C. and 530 m.m. will occupy what
volume at 18.7° C. and 590 m.m.?

21. 1,704 c.c. of nitrogen at 11° C. and 760 m.m. are brought to a
temperatm^ of 27° C. and a pressure of 900 m.m. What is the volume?

22. 271 c.c. of hydrogen at 269° and 900 m.m. are cooled to -51° C,
and the pressure decreased to 666 m.m. Calculate the final volume.

4. The effect of water vapor on the volume of a mass of gas. —
Suppose that we have 100 c.c. of dry oxygen confined over
mercury in a graduated tube. Let us admit a drop of water

CHEMICAL CALCULATIONS

383

and allow the oxygen to saturate itself with moisture. Clearly,
the volume of gas in the tube must increase, for the water
vapor will occupy space. The result is the same as though
we had introduced a little nitrogen or some other gas into
the tube, and allowed it to mix with the oxygen.

The volume can be kept 100 c.c. by increasing the pressure
imder which the gas is measured. But if this is done, the
total pressure cannot be considered as exerted upon the oxy-
gen in the tube, for the water vapor is also present. Hence,
the pressure imder which the gas really exists, and is measured,
is less than the total pressure. How much less?

The pressure which saturated water vapor exerts at va-
rious temperatures is given in the table. When a gas is
measured over watery or when it is measured saturated with
water, the pressure which water vapor exerts at the temperature
of measurement must he ascertained from the table and deducted
from the total pressure. The remainder will he the pressure
under which the gas is really measured.

Vapor Pressure op Water

Vapor

Tempera-

pressure in

Tempera-

pressure in

Tempera

pressure in

ture, Cen-

m.m. of

ture, Cen-

m.m. of

ture, Cen-

m.m. of

tigrade.

mercury.

tigrade.

mercury.

tigrade.

mercury.

—10

2.09

10.46

24.99

— 5

3.11

11.16

26.51

4.60

11.91

28.10

+ 1

4.94

12.70

29.78

5.30

13.54

31.55

6.69

14.42

41.83

6.10

15.36

54.91

6.53

16.35

91.98

7.00

17.39

148.79

7.49

18.50

233.09

8.02

19.66

354.64

8.57

20.89

525.45

9.17

22.18

100

760.00

9.79

23.55

384 AN INDUCTIVE CHEMISTRY

The vapor pressure of water for a temperature not given
in the table can easily be found by calculation. Thus, sup-
pose it is required to find the vapor pressure for the tem-
perature of 32.6*. The increase in vapor pressure from 30**
to 35* is 41.83-31.56 =10.28 m.m. Hence, the increase

2 6

from 30* to 32.6** will not be far from 10.28 X— , or 6.14

m.m., and the vapor pressure for 32.6* will be about 36.69
m.m. It will not be exactly 36 . 69 m.m., because, in the cal-
culation, it is assumed that the vapor pressure increases
proportionally with the temperature, which is not the case,
but for small differences of temperature the error is small.

Problems

33. A mass of air at 15.3^ C. and 747.2 m.m., measured over water ^
occupied a volume of 82 . 4 c.c. What volume would it occupy dry and
at standard conditions?

Solution : From the table we observe that water vapor at 15° C. exerts
a pressure of 12 . 7 m.m. and at 16° C. a pressure of 13 . 54 m.m . Hence
its pressure at 16.3° C. must « 12.9 m.m.
The pressure under which the gas is really measured is

747.2 — 12.9 = 734.3 m.m.

The rest of the calculation is the same as in the preceding problems:

_ ^ 273 734.3

82.4 X rrr-r X -z—- = 75.39 c.c.
288.3 760

34. 11 . 41 c.c. of a mixture of oxygen and hydrogen are measured over
water at 14° C. and 743 m.m. Calculate the volume imder standard
conditions.

25. 112 . 1 c.c. of nitrogen saturated with water at 16° C. and 744 m.m.
will occupy what volume dry and under standard conditions?

26. The gas-holder of a gas-works contains 4,500 cu. m. of illimiinat-
ing gas, confined over water. The temperature is 9° C. and the pressure
776 m.m. How many cubic meters would the gas measure imder stan-
dard conditions?

37. 100 c.c. of oxygen are confined over water and measiu'ed at 14° C.
and 756 m.m. What will be the volume when the gas is dried and placed
under standard conditions?

CHEMICAL CALCULATIONS 385

28. A gas-holder contains 10 1. of air confined over water at 20*' C.
and 756 m.m. What will the gas measure when dried, other conditions
remaining the same?

506. Calculation of the Percentage Composition from the
Fonnula (p. 89). — Let it be required to calculate the percent-
ages of iron and sulphur in pyrite. The formula FeS2 informs
us that the pure mineral contains 66 parts by weight of iron
and 64 of sulphur in 56 + 64 or 120 parts by weight.
Hence the percentage of iron must be:

56 ,^^ ,^ ^^ , . . , .

— X 100 = 46.67 per cent., and that of sulphur,
120 f f f }

— X 100 = 63.33 per cent.
120

Problems

Calculate the percentage composition of the following substances.
The amount of each element should be obtained by an independent cal-
culation — ^never by subtracting the sum of the others from 100. State
the result to two decimal places. If the third decimal place is greater
than 5, add 1 to the second; if less than 5, discard it. Check the results
by ascertaining whether ^q sum of the percentages for each compoimd
equals 100. Use the approximate atomic weights in all problems.

29. Mercuric oxide, HgO. 34. Water, H2O.

30. Mercuric chloride, HgCla. 35. Mercurous chloride, HgCl.

31. Potassium chlorate, KClOs. 36. Sodium chloride, NaCl.

32. Manganese dioxide, MnOs. 37. Nitric acid, HNOa.

33. Potassium nitrate, KNOs. 38. Sugar, C12H22O11.
Calculate the percentage of water only in the following:

39. Copper sulphate, CUSO45H2O.

40. Potassium alum, K2S04Al2(S04)824 H2O.

41. Chrome alum, K8S04Crs (804)3 24 H2O.

42. Ferrous sulphate, FeS04 7H2O.

43. Calculate the percentage of iron in the following important iron ores :

Hematite, FeiOs; magnetite, Fe804; Siderite, FeCOa; Limonite,
2 Fe^Os 3 H2O.

507. Calculation of the Fonnula from the Percentage
Composition (p. 90). — ^Let it be required to obtain the form-
ula of copper glance. The mineral contains:

386

AN INDUCTIVE CHEMISTRY

Sulphur 20.13 per cent.
Copper 79.87 per cent.
Total 100 per cent.

Divide the percentage of sulphur by the atomic weight of
sulphur:

20.13 + 32 = 0.629.

Divide the percentage of copper by the atomic weight of
copper:

79.87 4- 63.6 = 1.258.

The molecule of the mineral therefore contains copper and
sulphur atoms in the proportions 1.258 : 0.629. But
1.258 : 0.629 : : 2 : 1, hence the simplest formula of copper
glance is CusS. The slight errors which always exist in
percentages determined by chemical analysis do not inter-
fere with the calculation.

Problems
Calculate the simplest formulas of the following:

44. Hydrogen
Chlorine

45. Nitrogen
Oxygen

46. Carbon
Hydrogen
Oxygen

47. Mercury
Iodine

48. Calcium
Carbon
Oxygen

51. Silver 56.40 per cent.
Chlorine 18.52 per cent.
Oxygen 25.08 per cent.

If silver is univalent, what must be
the formula of chioric add?

52. Sodium 32.9 per cent.
Aluminium 12.9 per cent.
Fluorine 54.2 per cent.
(52) is the mineral cryolite,

53. Sulphur 35.87 per cent.
Copper 34.40 per cent.
Iron 30.47 per cent.

(53) is chalcopyrUe, This is an ac-
tual analysis, and the percentages
do not add to 100.

2.74 per cent.
97.26 per cent.
30.43 per cent.
69.67 per cent.
40.00 per cent.

6.67 per cent.
53.33 per cent.
44.07 per cent.
55.93 per cent.
40.00 per cent.
12.00 per cent.
48.00 per cent.

49. Potassium 52.35 per cent.
Chlorine 47.65 per cent.

50. Potassium 45.9 per cent.
Nitrogen 16.5 per cent.
Oxygen 37.6 per cent.

508. Calculations of Weights — (p. 91).

54. How many grams of mercury and how many of oxygen can be
obtained by heating 25 g. of mercuric oxide?

HgO — >- Hg + O

CHEMICAL CALCULATIONS 387

55. How many grams of oxygen can be obtained by heating 10 g. of
potassium chlorate?

KClOa — >- KCl + 3 O

56. How many grams of potassium chlorate are needed to prepare 12 g.
of oxygen?

57. What is the weight of the hydrogen which escapes when 0.5 g.
of sodium acts upon water?

Na + H,0 — >■ NaOH + H

58. What is the cost of preparing a kilogram of hydrogen from zinc
and sulphuric acid? Suppose that the price of zinc is 44 cts. per kilo,
and that of sulphuric acid 6 cts. per kilo.

Zn + H2SO4 — >- ZnS04 + H2

59. How many grams of zinc oxide are produced by burning 5 g. of

zinc?

Zn + O >- ZnO

60. How many grams of magnesium oxide are produced by burning
12 g. of magnesium ribbon?

Mg + O — >- MgO

61 • What is the least weight (in grams) of phosphorus that will
completely remove the oxygen from 200 c.c. of air? Assume that air
contains 21% of oxygen by volume or 23% by weight. Weight of 1
liter of oxygen = 1.43 grams.

2P + 50 — >- PiOs

6a. How many grams of copper wire can be changed to cupric oxide
by heating in a liter of air?

Cu + O — >- CuO

63. What would be the increase in weight of 30 g. of powdered iron if
converted (a) into ferrous oxide FeO; (6) into ferric oxide Fe208?

64. How many grams of potassium chlorate are necessary to furnish
enough oxygen to convert 30 g. of copper into cupric oxide?

65. How many grams of oxygen can be obtained by the catalytic
action of platinum upon 100 g. of a 5% solution of hydrogen peroxide?

H,0, — >- H2O + O

66. How many grams of pure hydrogen peroxide will convert 10 g.
of lead sulphide into lead sulphate?

PbS + 4H,02 — >- PbS04 + 4HiO

388 AN INDUCTIVE CHEMISTRY

67. How many gramB of ammonium chloride are necessary to prepare
3 kg. of a 30% anmionia solution?

2 NH4CI + Ca(OH), — >- CaCl, + 2 HiO + 2 NH3

68. How many grams of nitrous oxide can be made by heating 20 g.
of ammonium nitrate?

NHiNOs — >- N2O + 2 HiO

69. How many kilograms of a 30% solution of hydrochloric acid can
be made from 50 kg. of sodium chloride?

2 NaCl + H,S04 >- NaaS04 + 2 HQ

70. How many grams of potassium bromide and how many of silver
nitrate are needed to prepare 12 g. of silver bromide?

AgNOi + KBr — >- AgBr + KNOi

71. How many grams of bromine are needed to make half a kilogram
of potassium bromide? Assiune that all the bromine is finally obtained
as KBr.

73. How many grams of sodium bromide must be heated with sul-
phiuic acid and manganese dioxide to obtain 10 g. of bromine?

2 NaBr + MnO,+ 3 H2SO4 — >-2 Na HSO4 + MnS04 + 2 H,0 + Br«

73* 5 g. of sulphur are burned with an excess of air and the combus-
tion products passed over finely divided platinum. How many grams
of sulphur trioxide are produced.

S + O, — >- SOi
SO, + O — >- SOs

74. 80 g. of a solution of sulphuric acid are exactly sufficient to dis-
solve 22 g. of cupric oxide. What was the percentage by weight of
sulphuric acid in the original solution?

CuO + H,S04 — >- CUSO4 + H,0

75. 30 kg. of a phosphate rock, which contains 58% of tri-calcium
phosphate, Ca3(P04)2, are heated in an electric furnace with sand and
coke. How many grams of phosphorus are obtained?

Ca3(P04)2 + 3 SiOa + 5 C — >- 3 CaSiOa + 5 CO + 2 P

76. 50 kg. of impure stibnite containing 60% of ShSz are heated with
iron. How many kilograms of antimony are obtained?

SbaSa + 3 Fe — >- 3 FeS + 2Sb

77. 310 g. of borax-crystals are dissolved in a small quantity of water
and sulphuric acid is added. How many grams of sulphuric acid should
be used and how many grams of boric acid are obtained?

Na2B407lO H2O + H2SO4 — >- Na4S04 + 4 HbBOs + 5 H,0

CHEMICAL CALCULATIONS 389

78. I have 100 kg. of tin ore containing 3% of tin dioxide. How
many grams of tin can be obtained from it, assuming that 5% of the tin
is lost during the extraction?

SnOa + C >- Sn + CO2

79. How many grams of tin and how many of a 30% solution of
hydrochloric acid are needed to prepare 100 g. of crystallized stannous
chloride SnCU 2H2O?

Sn + 2 HCl + 2 H2O >- SnCU 2 H2O + H,

80. How many kilograms of potassium nitrate can be made from a
metric ton of sodimn nitrate and how many kilograms of potassium
chloride must be used? A metric ton = 1000 kg.

NaNOa + KCl >- NaCl + KNO3

81. Calculate the loss in weight when 15 g. of pure marble are heated
until the chemical change is complete.

CaCOs >• CaO + CO2

82. An excess of barium chloride solution was added to 32 g. of a
solution of sulphuric acid. The barium sulphate obtained weighed
11.43 g. Calculate the percentage of sulphuric acid in the sulphuric
acid solution.

BaCl, + H2SO4 — >- BaS04 + 2HC1

83. 1.4 g. of an alloy of copper and silver were dissolved in nitric
acid and hydrochloric acid was added. The silver chloride AgCl, which
was precipitated, weighed 1.6 g. How many grams of silver and cop-
per were present in the sample and what was its percentage composition?

84. How many kilograms of a 10% solution of acetic acid can be
made from 10 kg. of 80% alcohol?

CiHaO + O, — >- C2H4O4 + HjO

85. Calculate the percentages of carbon and hydrogen in the first
five members of the methane series of hydrocarbons. Their general
formula is CnHjn+i.

86. Anhydrous sodium carbonate has the formula Na^COs. If lOg.
of the crystallized salt lose 6.29 g. of water on the appHcation of heat,
how many molecules of water of crystallization were present?

87. Anhydrous barium chloride is BaCls. If 5 g. of the crystallized
salt leave, after being heated, a residue of 4.26 g., how many molecules
of water of crystallization were present?

88. Anhydrous zinc sulphate is ZnSOi. If the crystallized salt loses
43.8% of its weight when heated, what is its formula?

390 AN INDUCTIVE CHEMISTRY

89, Mercuric oxide is heated (a) alone ; (6) with carbon ; (c) with hydro-
gen. Calculate the weight of all the products if 10 g. of mercuric oxide
were used.

(a) HgO >- Hg + O

(6) 2 HgO + C >- 2 Hg + CO,

go. How many grams of chlorine can be obtained by the electro^rsiB
of a solution containing 100 g. of sodium chloride?

91. The hydrogen obtained by dissolving 12.1 g. of zinc in hydro-
chloric acid is passed over warm mercuric oxide. How many grams of
water and how many of mercury are produced?

Zn + 2HC1 >- ZnCla + H

HgO + H, >- H,0 + Hg

93. How many grams of ammoniimi nitrate would yield enough
nitrous oxide to bum 24 g. of carbon?

NH4NO8 — >- N,0 + 2H,0
C + 2 N2O — >- CO, + 2 N,

509. Volumes. — The gases are at S.T.P. unless otherwise
stated.

How many liters of hydrogen are produced when 32.75
grams of zinc are dissolved in sulphuric acid?

Zn + H2SO4 — >- ZbSOa + H2,

65.5 grams. 22.4 liters

hence: 65.5 : 32.75 : : 22.4 : x x =^ 11.2 liters

93. How many liters of hydrogen are formed by the action of 3 grams
of sodiimi upon water?

Na + H2O >- NaOH + H

94. How many grams of zinc and how many of 90% suphuric acid
are needed to fill with hydrogen a gas holder of 15 1. capacity?

95. How many liters of a mixture of hydrogen and oxygen are formed
by the electrolysis of 20 g. of water?

96. A liter of the mixed gases of (95) is exploded. How many cubic
centimeters of water at 4° are obtained?

97. How many grams of water result from the burning of 12 1. of
hydrogen?

98. How many times denser is liquid water than hydrogen gas?
1 1. hydrogen = 0.09 g.

99. How many times denser is copper than hydrogen? Specific
gravity of copper = 8.9.

CHEMICAL CALCULATIONS 391

100. A solution of hydrochloric acid was made by dissolving 450 1.
of hydrogen chloride in one liter of water. What was the percentage
by weight of hydrogen chloride in the solution?

loi. How many grams of alcohol and how many liters of carbon
dioxide result from the fermentation of a kilogram of grape sugar?

CeHiaOe — >■ 2 CjHeO + 2 CO2

102. How many liters of oxygen can be made by heating 50 g. of
mercuric oxide?

2 HgO — >■ 2 Hg + O,

103. How many cubic centimeters of oxygen are obtained by heating
one gram of potassium chlorate?

2KCIO3 — >■ 2KC1 + 3O2

104. How many grams of mercuric oxide are needed to prepare 12
liters of oxygen?

105. How many kilograms of oxygen and how many of nitrogen are
contained in a room 8 meters long, 6 meters wide, and 4 meters high?
Assume 23% by weight of oxygen in air. Take the balance as nitrogen.
Weight 1 Uter air = 1 .293 grams.

106. A certain blast furnace requires daily 600,000 kilograms of air.
How many cubic meters at S.T.P. does this make?

107. How many liters of oxygen are required to bum 1 g. of pure
charcoal and how many Uters of carbon dioxide result? •

C + O2 >- CO2

108. How many grams of water are formed by the burning of 5 I.
of hydrogen?

109. How many Uters of hydrogen must be burned to produce 5 g.
of water?

no. How many liters of air are necessary to bum a kilogram of a
coke which contains 82% of carbon?

111. How many liters of nitrous oxide can be made by heating 75 g.
of ammoniimi nitrate?

NH4NO3 — >■ N2O + 2H2O

112. How many liters of hydrogen chloride can be made from 25 g.
of sodiiun chloride?

2 NaCl + H2SO4 — >■ Na2S04 + 2 HCl

113. How many grams of salt must be electrolyzed to yield 10 1.
of chlorine?

392 AN INDUCTIVE CHEMISTRY

114. How many grams of ammonium chloride are needed to furnish
10 1. of hydrogen chloride?

2 NH4CI + H2SO4 >- (NH4) SO4 + 2 HCl

X15. If a sample of bleaching powder liberates, when treated with
acids, 32% of its weight of chlorine, how many liters of chlorine, Clj,
can be obtained from a kilogram?

116. How many grams of phosphorus are needed to remove all the
oxygen from a cubic meter of air? Air contains 23% oxygen by weight.
1 1. air weighs 1 . 293 g.

2 P + 6 O >- P/36

117. How many liters of hydrogen sulphide can be obtained from
150 g. of a sample of iron sulphide which contains 60% FeS?

FeS + 2 HCl — >■ FeCl, + H2S

1x8. The capacity of a room is 160 cu. m. and the air in it contains
0.03% of hydrogen sulphide. How many liters of chlorine are neces-
sary to destroy the odor?

H2S + CI2 — >■ 2 HCl + S

119. How many liters of sulphur dioxide are produced when 12 grams
of sulphur are burned?

S + O2 — >■ SO2

How many liters of oxygen are necessary?

120. A metric ton (1000 kg.) of pyrite containing 7% of foreign sub-
stances is burned in a lead-chamber plant. How many kilograms of
ferric oxide does the residue contain, and how many liters of sulphur
dioxide are produced? How many kilograms of 62% chamber acid
can be obtained?

2 FeSa + 11 >• FezOs + 4 SO^

SO2 + H2O + O — >■ H2SO4

121. How many grams of bromine can be obtained by passing
chlorine into 6 kg. of a liquid containing . 25% by weight of magnesium
bromide? How many liters of chlorine are necessary?

MgBrj + CI2 — >■ MgClj + Br,

122. How many grams of iodine can be obtained by leading chlorine
into 1 kg. of a solution containing 1% by weight of potassium iodide?
How many liters of chlorine are needed?

2 KI + CI2 >- 2 KCl + I,

CHEMICAL CALCULATIONS 393

123. How many liters of hydrofluoric acid can be made from 20 g.
of fluor-spar?

CaF, + H2SO4 — >• CaS04 + 2 HF

124. How many cubic centimeters of acetylene can be prepared from
10 g. of 90% calcium carbide?

CaC2 + 2 H2O — >• Ca(0H)2 + C2H2

125. How many cubic meters of air are needed to bum a metric ton
of anthracite coal which contains 95% of carbon? Air contains 21%
oxygen by volume.

C + O2 >• CO2

126. How many grams of water and how many liters of carbon dioxide
are produced by burning 2 1. of methane?

CH4 + 2O2 — >• CO2 + 2H2O

510. Volumes at Temperatures and Pressures other than
Standard. — How many liters of oxygen at 27** and under a
pressure of 740 m.m. can be made by heating 27 grams of
mercuric oxide?

2 HgO — >- 2 Hg + O2
432 grams 22.4 liters

Hence, for the volume of the oxygen at S.T.P. we have:

22.4 X 27
432

This must now be corrected for temperature and pressure.
The absolute temperature of 27'' is 273'' + 27'' = 300^
For the final volume we have:

27 300 760 ^ ^^ ,.

22-^ X i^ X ^ >< VTo = '-'^ '^'^^

The use of four-place logarithms greatly simplifies the cal-
culation.

127. How many liters of sulphur dioxide at 15° and 860 m. m. are
produced by burning 8 g. of sulphur?

S + O, — >• SO,

394 AN INDUCTIVE CHEMISTRY

128. How many liters of carbon dioxide at 15^ and 760 m.m. are pro-
duced by burning 6 g. of pure carbon?

C + O, >- CO,

129. How many liters of nitrous oxide at 15** and 800 J^.m, can be
obtained by heating 400 g. of ammonium nitrate?

NH4NO8 >- 2H,0 + N,0

130. How many liters of ammonia at 15° and 380 m.m. can be obtained
from 40 g. of anmionium chloride?

2 NH4CI + Ca(OH), >- CaCl, + 2 H,0 + 2 NH3

131. How many liters of air measured at 20° and 760 m.m. are re-
quired to bum 10 g. of pure carbon?

C + O, — >- CO,

132. How many liters of hydrogen sulphide measured at 16°. 5 and
754 m.m. are produced when 250 g. of iron sulphide are dissolved in
hydrochloric acid?

FeS + 2 HCl — >• FeCl, + H,S

133. How many liters of anmionia at 15° and 748 m.m. are produced
by heating 100 g. of sal ammoniac with slaked lime?

2 NH4CI + Ca(OH), — >• CaClj + 2 HjO + 2 NHs

134. How many grams of pure sal anmioniac and how many grams of
92.% sodiimi nitrite are needed to liberate 5 1. of nitrogen at 12°. 5 and
765 m.m.?

Na NO2 + NH4 CI — >- Na CI + 2 H2O + Nj

135. How many liters of nitrous oxide at 15° and 700 m.m. can be ob-
tained by heating 200 g. of ammonium nitrate?

NH4NO3 >- N,0 + 2 H,0

136. How many liters of nitric oxide at 15° and 740 m.m. can be ob-
tained by dissolving 80 g. of copper in nitric acid?

3 Cu + 8 HNO3 >- 3 Cu(N03), + 4 H,0 + 2 NO

137. A piece of pure marble weighing 10 g. is heated to complete de-
composition, (a) How many grams of lime remain? (6) How many
liters of carbon dioxide at 20° and 740 m.m. escape?

CaC03 >- CaO + CO,

138. How many liters of carbon dioxide at 12° and 750 m.m. are pro-
duced by dissolving 20 grams of pure marble in hydrochloric acid?

CaCOa + 2 HCl — >• CaCl, + H,0 + CO,

CHEMICAL CALCULATIONSb 395

511. Simple Calctilations of Atomic Weights. — Berzelius
found that 10 g. of lead yielded 10.77 g. of lead monoxide,
PbO. What is the atomic weight of lead?

The weight of oxygen which unites with 10 g. of lead is
10.77 — 10 = 0.77 g.

The atomic weight is the number of grams of lead which in
lead monoxide is united with 16 g. of oxygen. Hence we
have:

0.77 : 10 : : 16 : a; a; = 207.9

1 g. of tin was converted into tin dioxide Sn02. The in-
crease in weight was 0.271 gram. What is the atomic
weight of tin? The atomic weight is the number of grams
of tin which, in tin dioxide, is combined with 32 g. of oxygen.
Hence:

0.271 : 1 :: 32 : a; a; = 118

Stas found that 101.519 g. of silver, when heated in
chlorine, gave 134. 861 g. of silver chloride, AgCl. Required,
the atomic weight of silver.

The weight of chlorine which combined with the silver
is 134.861-101.519 = 33.342 g. Taking the atomic
weight of chlorine as 35.5 we have:

33.342 : 101.519 : : 35.5 \ x x =- 108.1

139. Dumas and Stas obtained 59.3765 g. of carbon dioxide, COj, by
burning 16 . 192 g. of pure carbon. What is the atomic weight of car-
bon, if O = 16?

140. Berzelius oxidized 25 g. of lead and obtained 26.925 g. of lead
monoxide, PbO. What is the atomic weight of lead?

141. Berzelius heated 43.9650 g. of lead monoxide in hydrogen and
obtained 40.8125 g. of lead. What is the atomic weight of lead?

PbO + H2 >- Pb + H2O

142. If 118.3938 g. of mercuric oxide, HgO, yield, when heated,
109 . 6308 g. of mercury, what is the atomic weight of mercury?

143. 88.5832 g. of mercuric sulphide, HgS, jrield, when completely
decomposed, 76.3725 g. of mercury. What is the atomic weight of
mercury?

396 AN INDUCTIVE CHEMISTRY

144. 0.5 g. of sine, when dissolved in hydrochloric acid, liberated
183 . 7 c.c. of hydrogen measured over water at 15* and 760 nun. What
is the atomic weight of sine, if H « 1.008?

Zn + 2 HCl — >- ZnCl, + H,

145. If 1 g. of zinc set free 366 c.c. of hydrogen, measured over water
at 9** and 748 m.m., what is the atomic weight of sine?

146. The specific heat of lithium is 0.941, of potassium 0.166, of
chromium 0. 121, of iron 0. 114, of cobalt 0. 107, of nickel 0. 108, of tin
0.054, of mercury 0.032 and of lead 0.031. Assuming that the prod-
uct of specific heat and atomic weight is, in each case, 6 . 4, calculate the
atomic weights of these metals. See Law of Dulong and Petit, p. 228.

Miscellaneous Problems

147. If 27.396 g. of water contain 24.352 g. of oxsrgen, what is the
percentage composition of water?

148. 4 g. of hydrogen are slowly passed through a glass tube contain-
ing a large quantity of cupric oxide, heated to redness, (a) How many
grams will this tube lose in weight? (6) How many grams of water
will be formed?

149. 10.98 g. of a solution of potassium chlorate saturated at 18^
were placed in a weighed dish and evaporated to dryness. The po-
tassiimi chlorate which remained weighed . 7025 g. How many grams
of potassium chlorate were contained in 100 g. of the solution?

150. Using the figures of problem 149, calculate how many grams of
potassium chlorate 100 g. of water at 18° will dissolve.

151. Using the same figures, calculate how many grams of water at
18* are needed to dissolve 1 g. of potassium chlorate.

152. A solution of table-salt saturated at 15° contained 26.39% of
salt. How many grams of salt will 100 g. of water dissolve at 15°?

153. If 75 c.c. of oxygen could be changed completely to ozone, what
volume of ozone could be obtained?

3 0, >- 2 08

154. 115 c.c. of oxygen were partly converted into ozone. The
volume contracted to 110 c.c, but, when the gas was gently heated, the
original volume was restored. Calculate (a) the number of cubic
centimeters of ozone which had been produced, and (6) its percentage by
volume.

155. 160 c.c. of oxygen containing ozone were heated. The volume
became 170 c.c. (a) How many c.c. of ozone, and (6) what percentage
of it by volume, were present?

CHEMICAL CALCULATIONS 397

156. Calculate the percentage composition of (a) sodium carbonate
Na2C03; (6) crystallized sodium carbonate, Na2C08lO H2O. In (6)
calculate watery not hydrogen.

157. How many grams of sodium are necessary to decompose 36 g.
of water? How many grams of hydrogen are liberated?

Na + H2O >- NaOH + H

158. How many grams of sodium can be obtained by the electrolysis
of 20 g. of sodiimi hydroxide?

NaOH — >- Na + O + H

159. A piece of sodium was placed in water. 500 c.c. of hydrogen,
measured at S.T.P. escaped. What was the weight of the sodium?

160. How many grams of chlorine can be obtained by heating 12.5 g.
of manganese dioxide?

Mn02 + 4 HCl >- MnCk + 2 H2O + CI2

161. How many grams of manganese dioxide are needed to>make 25
g. of ^chlorine from hydrochloric acid?

162. How many grams of a hydrochloric acid solution containing 20%
HCl are needed to liberate 100 g. of chlorine with manganese dioxide?

163. 20 c.c. of chlorine were mixed with 16 c.c. of hydrogen and the
mixture exploded. What volumes of what gases remained in the vessel?

H2 + CI2 >- 2 HCl

164. Hydrogen was burned in chlorine and the hydrogen produced
collected. It weighed 146 g. How many grams of both gases had been
consmned?

165. 50 g. of sodium hydroxide are dissolved in water and the solu-
tion mixed with a solution containing 50 g. of pure hydrochloric acid.
What substances and how many grams of each are contained in the
resulting Uquid? Do not calculate water.

NaOH + HCl — >- NaCl + H2O

166. 32.75 g. of zinc are dissolved in hydrochloric acid. How many
grams of zinc chloride and how many of hydrogen are produced?

Zn + 2 HCl >- ZnCl2 + H2

167. 40 g. of magnesium are dissolved in hydrochloric acid. How
many grams of hydrogen and how many of magnesium chloride are
formed?

Mg + 2 HCl — >- MgCfe + H2

398 AN INDUCTIVE CHEMISTRY

1 68. Determine the name and formula of a compound having the
following composition:

Sodium 21.60
Chlorine 33.33
Oxygen 45.07

i6g. 25 g. of pure marble are dissolved in hydrochloric acid. How
many grams of each product is formed? How many grams of hydro-
chloric acid, HCl, are consumed?

CaCX)i + 2 HCl — >• CaCli + HjO + CO2

170. 2 g. of finely divided copper were heated in oxygen. 2 . 5063 g.
of cupric oxide, CuO, were produced. Calculate the atomic weight of
copper.

171. 16 . 7 c.c. of air were confined over mercury in a eudiometer and
enough hydrogen added to make the volume 30 c.c. After explosion,
the volume was 19.5 c.c. What percentage of oxygen by volume did
the air contain^

172. 20 c.c. of air are mixed with 10 c.c. of hydrogen and the spark
is passed. After the explosion, what volumes of what gases remain in
the tube? Assume that air contains 21 per cent by volume of oxygen.

173. 2 1. of air were passed over hot copper. The increase in weight
of the copper was .6 g. What was the percentage of oxygen by weight
in the air? Assume the weight of 1 1. of air to be 1 . 293 g.

174. What weight of nitrogen can be obtained by heating 13.8 g.
of sodium nitrate, NaN02, with the required quantity of ammonium
chloride, NH4CI? How many grams of ammonium chloride are needed?
What weights of salt and of water are formed? See problem 134.

175. 856 g. of ammonium chloride are heated with sodium hydroxide.
How much ammonia by weight escapes?

NH4CI + Na OH — >- Na CIH- H2O + NH5

176. Calculate the percentage composition of:

a. Ammonium chloride, NH4CI.

b. Ammonium nitrate, NH4NO3.

c. Ammonium sulphate, (NH4)2S04.

d. Ammonium hydroxide, NH4OH.

177. When a stream of electric sparks is passed through ammonia it
is decomposed, two volumes yielding one volume of nitrogen and three
volumes of hydrogen. What volumes of nitrogen and hydrogen are
formed when 300 c.c. of ammonia are treated in this way?

CHEMICAL CALCULATIONS 399

178. 100 c.c. of ammonia are decomposed by a stream of sparks,
(a) What volume of oxygen must be added to the resulting mixture to
combine with the hydrogen and produce water? (6) After the water
has condensed, what gas will remain in the tube, and how much?

179. 32 c.c. of ammonia are decomposed by sparks. 50 c.c. of oxygen
are added, and the mixture is caused to explode. What volumes of what
gases are left?

180. An unknown volume of ammonia is decomposed in a eudiometer,
an unknown volume of oxygen is mixed with it, and the mixture ex-
ploded. After the explosion the contraction in volume is 18 c.c. and
the tube still contains some oxygen, (a) What volume of ammonia was
taken in the first place, and (6) what volume of nitrogen was left in the
tube?

i8i. Ammonium chloride is heated in a flask with sodium hydroxide
and the ammonia passed into 31.5 g. of pure nitric acid. How much
ammonium chloride must be used in order to convert all the nitric acid
into ammonium nitrate?

182. What weight of nitric acid containing 80 per cent. HNOa is
necessary to dissolve 10 g. of cupric oxide?

CuO + 2 HNO3 — >- Cu(N03)2 + H2O

183. What weight of pure nitric acid would contain 50 g. of oxygen?

184. Assuming that the density of pure nitric acid is 1 . 5, how many
grams of oxygen do 3 1. of it contain?

185. How many grams of nitric acid can be obtained (a) by heating
200 kilos of sodium nitrate with sulphuric acid; (6) by heating 200 kilos
of potassium nitrate with sulphuric acid?

NaNOs + H2SO4 — >- NaHS04 + HNOa
KNO3 + H2SO4 — >■ KHSO4 + HNO3

186. I require 120 g. of cupric oxide. How many grams of crystal-
lized cupric nitrate must be heated to redness to make it?

Cu(N03)23H20 — >- CuO + 2 NO2 + O + 3 H2O

187. How many grams of nitric acid are needed to convert 400 g. of
potassium hydroxide into potassium nitrate?

KOH + HNO3 >- KNO3 -h H2O

188. Calculate the formula of a compound having the following
composition:

9.09 per cent nitrogen;
20.77 per cent oxygen;
70. 13 per cent silver.

400 AN INDUCTIVE CHEMISTRY

z89. Calculate the molecular weights of the following compounds:

a. Sugar, CnHnOii;

6. Bismuth nitrate, Bi(NO|)i;

c. Nitroglycerin, C|H6(N0|)i;

d. Glucose, CeHisOe.

XQO. What is the weight in grams of 28 1. (a) of nitrous oxide; (b)
of nitric oxide?

191. What is the volume in liters (a) of 11 g. of nitrous oxide; (6) of
5 g. of nitric oxide?

19a. How many liters of hydrogen are needed to form water with the
oxygen (a) of 22 1. of nitrous oxide; (6) of 22 g. of nitrous oxide?

N,0 + H, >- H,0 + N,

193. What is the volimie of 13 g. of nitric oxide?

194. How many liters of nitrous oxide — measured at standard con-
ditions—can be made from 80 g. of ammonium nitrate? Solve by in-
spection.

NH4NOS >- N2O + 2 HjO

195. How many grams of anunonium nitrate are needed to make 80 1.
of nitrous oxide?

196. How many grams of anmionium nitrate are needed to make
4,000 c.c. of nitrous oxide?

197. How many grams of copper are needed to produce 30 1. of nitric
oxide?

3 Cu + 8 HNOs >- 3 Cu(N08)i + 4 Hrf) + 2 NO

198. How many grams of ammonium nitrate are needed to produce
10 1. of nitrous oxide?

199. How many liters of nitrous oxide at 15° C. and 700 m.m. can be
obtained by heating 100 g. of ammonium nitrate?

200. How many liters of nitric oxide at 13° and 740 m.m. is obtained
by dissolving 40 g. of copper in nitric acid?

201. 10 g. of pure sodium hydroxide are dissolved in water, (a) How
many grams of nitric acid must be added to make the solution neutral?
(&) How many grams of sodium nitrate would be obtained if this was done?

202. I have a solution which contains just 40 g. of pure sodium
hydroxide in 1 liter. Calculate the quantities by weight of (a) HCl, (6)
HNO3, and (c) HsS04, which will be required to neutralize 1 c.c. of it.

203. 15.75 g. of nitric acid are mixed with 23. 25 g. of sodium hydrox-
ide, both dissolved in water. What two compounds does the solution
contain and how many grams of each? Do not calculate water,

204. In ascertaining the strength of a dilute solution of HCl, 50 c.c.
of it were measured out and neutralized with a solution of sodium

CHEMICAL CALCULATIONS 401

hydroxide containing . 003 g. of NaOH in 1 c.c. 40 c.c. of the sodium
hydroxide solution was required. What weight of HCl was contained in
1 c.c. of the hydrochloric acid?

ao5. 30 c.c. of a solution of potassium hydroxide containing .01 g.
of KOH in 1 c.c. was needed to neutralize 40 c.c. of a solution of HCl.
How many grams of HCl did 15 c.c. of the hydrochloric acid solution
contain?

ao6. 20 c.c. of a solution containing .005 g. of KOH in 1 c.c. just
neutralized 20 c.c. of a solution of hydrochloric acid. How many grams
of HCl did 15 c.c. of the latter contain?

207. How many grams of potassium are required to liberate from
water enough hydrogen to combine with 3 g. of oxygen?

ao8. How many liters of oxygen are needed to combine with the
hydrogen given off by the action of 9.75 g. of potassium on water?

209. How many grams of (a) potassium carbonate must be heated
with how many grams of (6) pure charcoal to produce 9.75 g. of
potassium, and (c) what volume of carbon monoxide would be liberated?

KjCOa H-2C = 3 CO +2K

310. Calculate the percentage composition (a) of silver chloride,
AgCl; (6) of silver sulphide, AgsS.

an. Calculate the formula of a compound of the following composi-
tion:

SUver 65.45

Sulphur 19.39

Arsenic 16 . 16

aza. When hydrogen is heated with silver chloride, silver is produced:

AgCl + H = HCl + Ag

If 52.65 c.c. of hydrogen produce 0.505 g. of silver, what is the atomic
weight of silver?

213. Calculate the percentage composition of silver acetate,
AgCHaO,.

a 14. How many grams of zinc are required to precipitate 5 g. of silver

from solution?

+ ++

2Ag + Zn = Zn + 2Ag

ax 5. A piece of pure marble weighing 50 g. is heated to complete
decomposition, (a) What is the formula and weight of the substance
which remains? (6) What gas escapes and what volume measured
at 20** and 740 m.m. (p. 313)?

ai6. How many tons of limestone must be heated to make 200 tons
of lime (p. 313)?

402 AN INDUCTIVE CHEMISTRY

217. Calculate the percentage composition (a) of barium sulphate,
BaS()4; (6) of barium carbonate, BaCOs.

ai8. 10 g. of barium carbonate are dissolved in hydrochloric acid,
(a) What volume of carbon dioxide is produced, and (6) how many
grams of cr3rstallized barium chloride, BaCls2 HsO, can be obtained
from the solution?

219. How many grams of barium sulphate can be made from 2 g.
of calcium sulphate, CaS04?

aao. 1.182 g. of barium carbonate were dissolved in hydrochloric
acid, and the solution precipitated with sulphuric acid. The barium
sulphate obtained weighed 1 . 398 g. Calculate the percentage of barium
in the barium carbonate.

aai. What volume of oxygen iiB needed to bum 9 g. of magnesium
to magnesium oxide MgO?

aaa. If 0.4 g. of magnesium liberated 391 c.c. of dry hydrogen at 13®
when treated with HCl, what is the atomic weight of magnesiimi ?

333. The electric current is passed through fused magnesium chloride,
MgCl2, until 14 g. of magnesium are obtained. What volume of
chlorine at standard conditions is liberated (p. 219)?

334. 768 g. of mercuric chloride are dissolved in water, (a) How
many grams of potassium iodide, KI, must be added to the liquid, and
(6) how many grams of mercuric iodide, Hgl^, will be obtained?

335. U mercurous chloride contains 84.93 per cent, mercury and 15.07
per cent, chlorine, and if the formula is HgiCU, what is the atomic weight
of mercury?

aa6. If mercuric chloride has the formula HgCls and contains 73.8
per cent, of mercury and 26.2 per cent of chlorine, what is the atomic
weight of mercury?

337. Calculate the percentage composition of borax, NajB407-
10 H2O. Calculate water^ not hydrogen.

228. If 6.75 g. of aluminium, when dissolved in hydrochloric acid
to AlCls, yield 8 . 4 1. of hydrogen, what is the atomic weight of the metal?

229. If 50 g. of litharge, PbO, contain 3 . 5862 g. of oxygen, what is
the atomic weight of lead?

230. What are the name and formida of a compound of the following
composition?

Lead 77. 52 per cent.

Carbon 4 . 49 per cent.

Oxygen 17 . 98 per cent.

231. How many liters of oxygen are needed to bum 93 g. of phos-
phorus to P2O6? A liter of oxygen = 1.43 grams.

232. 20 g. of phosphorus are burned in a vessel from which nothing is
allowed to escape. How many grams will the vessel increase in weight?

CHEMICAL CALCULATIONS 403

233. What volume of air is needed to bum 124 g. of phosphorus to
PaOs? Assume that air contains 21 per cent by volume of oxygen.

234. If 4 g. of phosphorus when burned yield 9 . 16 g. of P2O5, what is
the atomic weight of phosphorus?

235. 2 g. of crystallized copper sulphate, CUSO45H2O, are dissolved
in water, and it is required to precipitate aU the copper as CuS. How
many grams of iron sulphide and how many grams of hydrochloric acid
containing 25 per cent of HCl are needed to generate enough H2S for the
purpose (p. 167)?

236. (a) What volume Ox nydrogen sulphide is produced when 17 . 6 g.
of FeS are dissolved in HCl? (6) From how many grams of mercuric
chloride dissolved in water will this quantity of H2S precipitate the
mercury as mercuric sulphide (p. 167)?

HgCla + HaS = HgS + 2 HCl

237. What volume of air is needed to burn 500 g. of sulphur to SOi?
Assume that air contains 21 per cent of oxygen by volume.

238. What volimie of H2S escapes when 5 g. of iron sulphide are dis-
solved in HCl (p. 167)?

239. How many grams of iron sulphide are needed to make 59 liters
of HjS (p. 167)?

240. How many tons of sulphuric acid can be made fron 4 tons of
sulphur?

241. How many tons of sulphuric acid can be made from 40 tons of
pyrite, FeSa?

242. The density of sulphuric acid is 1.84. How many grams of
sulphur is there in 100 c.c. of it?

243. How many tons of sulphuric acid can be made from 100 tons
of pyrite containing 48 per cent, of sulphur?

244. 1 . 8752 g. of cobalt, when converted into cobalt sulphate, yielded
4.9472 g. What is the atomic weight of cobalt? Assume S = 32,
O = 16. The formula of cobalt sulphate is C0SO4.

245. How many grams of calcium fluoride and how many grams of
sulphuric acid containing 96 per cent H2SO4 are needed to make 12 g.
of pure hydrogen fluoride? See problem 123.

246. How many grams of calcium sulphate and how many grams
of hydrofluoric acid are formed when 50 g. of calcium fluoride are heated
with sulphuric acid? See problem 123.

247. Manganese dioxide is heated with hydrochloric acid, and the
chlorine passed in a solution of potassium iodide. How many grams of
iodine will be set free by the chlorine evolved when 12 g. of manganese
dioxide are used (p. 221)?

2 KI + CI2 — >-2KCl + la

404 AN INDUCTIVE CHEMISTRY

348. Under the same circumstances as in problem 247, how many
grams of manganese dioxide are needed to liberate 63 . 5 g. of iodine?

349. Under the same conditions as in the two preceding problems,
how many grams of iodine will be set free when 43.5 g. of manganese
dioxide are used?

350. What volume of hydrogen at 13* and 780 m.m. is needed to con-
vert 31 . 5 g. of FejOs into iron?

351. What volume of hydrogen at 14® and 740 m.m. is required to
change 20 g. of ferric oxide into iron?

352. If ferric oxide, FesOs, contains 70 per cent iron and 30 per cent
oxygen, what is the atomic weight of iron?

253. If ferrous oxide, FeO, contains 77 . 8 per cent iron and 22 . 2 per
cent oxygen, what is the atomic weight of iron?

354. The great German chemical works, the BadischeAnilinimdSoda
Fabrik, burns 190,000 T. of coal a year. If the coal contains 70 per cent
of carbon, and if there are 310 working dajrs in the year, how many tons
of COj escapes daily from the chimneys of the establishment?

355. What volume of carbon dioxide is formed by the burning of 30 1.
of carbon monoxide, and what volume of oxygen is required? Solve by
inspection.

256. What gas gives rise to the blue flame often seen playing over the
surface of a coal fire? How many grams of coal containing 90 per cent
of carbon would be needed to make 5,000 1. of this gas at 15® and 750
m.m.?

357. What voliune of carbon dioxide must be passed over glowing
charcoal to form 42 g. of carbon monoxide?

358. What is the volume (a) of 50 g. of carbon monoxide? (6) Of 50 g.
of carbon dioxide?

359. What volume of carbon dioxide would be produced by burning
a diamond weighing 3 g. in oxygen?

260. How many grams of carbon are there in (a) 2.8 1. of carbon
dioxide; (6) 2.8 1. of carbon monoxide?

261. What volimie of carbon dioxide at standard conditions is pro-
duced by dissolving 25 g. of marble in hydrochloric acid? See problem 138.

262. What volume of carbon dioxide at 12° and 750 m.m. is produced
by dissolving 35 g. of marble in hydrochloric acid? See problem 138.

263. What is the weight of 38 1. of methane at 31°?

264. What is the weight of 10 1. of acetylene?

265. How many grams of calcium carbide is needed to produce 5.61.
of acetylene? See problem 270, 1st equation.

366. A town is to be lighted with acetylene. It is calculated that the
consumption of the gas will be 70,000 1. per day. How many metric

C|IEMICAL CALCULATIONS 405

tons of calcium carbide will be required per month of thirtv days? See
problem 270, 1st equation.

267. How many grams of carbon are there in 32 1. of acetylene?

a68. How many grams of sodium acetate are needed to make 8 1. of
methane?

NaCHaO, + NaOH = CH4 + Na^COs

369. How many liters of oxygen at 10° and 780 m.m. are needed to
bum completely the methane obtained when 41 g. of sodium acetate are
heated with sodiimi hydroxide?

NaCjHaO, + NaOH = CH4 + Na«CO«
CH4 + 2O1 = CO, H- 2 H,0

270. Calcium carbide is treated with water and the acetylene burned.
28 1. of carbon dioxide at 15^ and 740 m.m. resulted from the combustion.
How many grams of calciima carbide were taken, and what volume of
o^gen at 15® and 740 m.m. was needed to bum the acetylene?

CaC + 2 H,0 = Ca(OH), + CiHt
C2H, + 50 = 2 CO, H- HiO

APPENDIX

I— THE METRIC SYSTEM

Length

1 inch = 2.54 centimeters. 1 centimeter = . 3937 inch.
For practical purposes it is useful to remember that 1 inch =
about 2| cm.

Volume

1 liter = 1000 cubic centimeters

1 liter = . 2642 gallon

1 liter = 1 . 057 quarts

1 pint = 0.473 liter

1 quart = . 946 liter

1 fluid ounce = 29 . 57 cubic centimeters

1 fluid dram = 3.7 cubic centimeters

For practical purposes it is useful to remember that 1 fluid
ounce = about 30 cubic centimeters. The drop is not a scien-
tific unit. Its volume depends upon the orifice and the speed
of dropping, as well as upon the nature of the liquid.

The amall test tubes used in the laboratory average about
15 cm. in length by 1.8 cm. in diameter. Their average capacity
is rather less than 40 cubic centimeters. It is convenient to
use them in rough measurements of volumes of liquids.

Weight

The gram is the weight of 1 cubic centimeter of water at 4°.
1 gram = 0.035 ounce (avoirdupois)
1 gram » 15.43 grains
1 ounce (avoirdupois) = 28.35 grams
1 kilogram = 1000 grams
1 kilogram = 2.2 pounds (avoirdupois)
1 metric ton = 1000 kilograms
1 metric ton = 2205 pounds (avoirdupois)

407

408 AN INDUCTIVE CHEMISTRY

It will greatly improve the quality of the student's laboratory
work if he will endeavor to form a fairly accurate idea of the
quantity denoted by a gram. To assist in this, the weights of
some common coins are given in grams. The weights are only
roughly approximate.

cent 3.1 grams

nickel 6 "

dime 2.5 "

quarter 6.6 "

half-doUar 13.3 "

silver dollar 26.6 "

II— THE CENTIGRADE SCALE OF THE THER-

MOMETER

Formula! for converting Fahrenheit degrees into Centigrade,
and the reverse.

F»=| (C°+32)
C° = 4 (F°-32)

The Conversion Table on the opposite page is due to Dr.
Leonard Waldo. The principle is the same as that of a table
of logarithms. Thus:

(1) What is the Fahrenheit equivalent of 1347^C?

Pass down the left-hand column to 1300°C. In the same
horizontal line in the 6th column to the right we find that
the Fahrenheit equivalent of 1340°C is 2444^F. In the
upper part of the right-hand margin we find that the
remaining 7°C = 12°.6F. Hence,

1347°C = 2444^F + 12^.6F = 2456^.6F

(2) What is the Centigrade equivalent of 3367°F?

The nearest temperature to 3367*'F in the table is
3362°F, which corresponds to ISSO^^C. In the lower part
of the right-hand margin we find that S^^F = 2°.78C.
Hence,

3367''F = ISSO^'C + 2°.78C = 1852*'.78C

APPENDIX

409

Centigrade-Fahrenheit Conversion Table

"?J<^

50-

T'nr

70 80

— 300

—ZOO

— O

-328

-148

+32

-346

-166

+ 14

-364

-184

-4

-382

-202

-22

-400

-220

-40

-418

-238

-68

-436

-266

-76

-464

-274

-94

-292
-112

-310
-130

104

122

140

168 176

194

ZOO
300

300
400

900

212
392
672

762

932

1112

1292
1472
1652

230
410
690

770

960

1130

1310
1490
1670

248
428
608

788

968

1148

1328
1608
1688

266
446
626

806

986

1166

1346
1626
1706

284
464
644

824
1004
1184

1364
1644
1724

302
482
662

842
1022
1202

1382
1662
1742

320
600
680

860
1040
1220

1400
1680
1760

338
618
698

878
1068
1238

1418
1698
1778

366
636
716

896
1076
1266

1436
1616
1796

374
664
734

914
1094
1274

1454
1634
1814

zooo

1832

1860

1868

1886

1904

1922

1940

1968

1976

1994

IIOO
I300

1300
Z400

ISOO
ZOOO

Z700

1500

Z900

2012
2192
2372

2662
2732
2912

3092
3272
3462

2030
2210
2390

2670
2760
2930

3110
3290
3470

2048
2228
2406

2688
2768
2948

3128
3308
3488

2066
2246
2426

2606
2786
2966

3146
3326
3606

2084
2264
2444

2624
2804
2984

3164
3344
3624

2102
2282
2462

2642
2822
3002

3182
3362
3642

2120
2300
2480

2660
2840
3020

3200
3380
3660

2138
2318
2498

2678
2868
3038

3218
3398
3678

2166
2336
2616

2696
2876
3066

3236
3416
3596

2174
2354
2634

2714
2894
3074

3264
3434
3614

3000

3632

3660

3668

3686

3704

3722

3740

3758

3776

3794

3100
3300
3300

3400
3500
3000

3700
3800
3900

3812
3992
4172

4362
4632
4712

4892
6072
6262

3830
4010
4190

4370
4660
4730

4910
6090
6270

3848
4028
4208

4388
4668
4748

4928
6108
6288

3866
4046
4226

4406
4686
4766

4946
6126
6306

3884
4064
4244

4424
4604
4784

4964
6144
6324

3902
4082
4262

4442
4622
4802

4982
6162
6342

3920
4100
4280

4460
4640
4820

6000
6180
6360

3938
4118
4298

4478
4668
4838

6018
6198
6378

3966
4136
4316

4496
4676
4866

6036
6216
6396

3974
4164
4334

4614
4694
4874

6064
6234
6414

3000

6432

6460

6468

6486

6604

6640

6668

6676

6594

3Z00
3300
3300

3400
3500
3600

3700
3800
3900

6612
6792
6972

6162
6332
6612

6692
6872
7062

6630
6810
6990

6170
6360
6630

6710
6890
7070

6648
6828
6008

6188
6368
6648

6728
6908
7088

6666
6846
6026

6206
6386
6666

6746
6926
7106

6684
6864
6044

6224
6404
6684

6764
6944
7124

6702
6882
6062

6242
6422
6602

6782
6962
7142

6720
6900
6080

6260
6440
6620

6800
69S0
7160

6738
6918
6098

6278
6468
6638

6818
6998
7178

6766
6936
6116

6296
6476
6666

6836
7016
7196

6774
6964
6134

6314
6494
6674

6864
7034
7214

zo 30

-^22.

«_K.

70 1 80 >

—21

2
3

4
6
6

7
8
9

F*»

1
2
3

4
6
6

7
8
9

10
11
12

13
14
16

16
17
18

1.8
3.6
6.4

7.2

9.0

10.8

12.6
14.4
16.2

10 18.0

66
1.11
1.67

2.22
2.78
3.33

3.89
4.44
6.00

6.56
6.11
6.67

7.22

7.78
8.33

8.89

9.44

10.00

EzAMPUs: 1347^ = 2444'F+12'.6F = 246tf».6F: 3367**?= 1860X;+2'.78C = 1852*.78C

410

AN INDUCTIVE CHEMISTRY

Some Important Temperatures

Centigrade.

-273**

-268^.5

-256°

-253°
-214°
-194°
-130°
- 39°.5
0°

10°.5
37°
60°
78°.5
10°
114°.5
120°
160°
232
320
327°
419°
448°
525°
660°
700°
772°
1000°
1064°
1100°
1200°
1375°
1500°

2000°
4000°
6000°

Fahrenheit

-459°. 4

-39°. 1
32°

212*

977°
1292°
1832°

2192°

2732°

3632°

7232°

10,832''

Absolute zero

Helium boils

Hydrogen freezes Boiling-points are
given for 760 mm. pressure.

Hydrogen boils

Nitrogen freezes

Nitrogen boils

Alcohol freezes (ethyl)

Mercury freezes

Ice melts

Sulphuric acid freezes

Average temp, of human body

Wood's fusible metal melts

Alcohol boils (ethyl)

Water boils (760 mm. pressure)

a-Sulphur melts

/5-Sulphur melts

Sugar (sucrose) melts

Tin melts

Cadmium melts

Lead melts »'

Zinc melts

Sulphur boils

First visible red heat

Aluminium melts

Dull red heat

Table-salt melts

Bright red heat

Gold melts

Copper melts

Bright orange heat

Temp, of glass-furnace

Bright white heat. Temp, of open-
hearth furnace

Temp, of Welsbach mantle

Temp, of electric arc

Temp, of sun

APPENDIX

411

III— NUMERICAL DATA FOR SOME OF THE MORE

IMPORTANT ELEMENTS.

Name.

Melting'
Point.

Boiling'
Point.

Specific
Oravity.

Specific
Heat.

• • • •

....

AS4

• • • •

Br2

• • • •

CI2

• • • •

« • • •

• • « •

H,
I>

• • • •

• • • «

• • • •

N,
0,

Valence.

Aluminium

660°

430°
-190°

2.58
6.7

0.22
0.052

Antimony

Argon

White heat
-185°
450°

(sublimes)

• 1100°?
63°

3, -5

Arsenic

5.7

9.9
3.2
1.6
2.2
3.5

1.33

(liquid)

6.8
8.9

(Uquid)

19.5

0.083

0.031

0.084

0.18

0.454

0.45

0.100
0.094

0.0316

3:5

Bismuth

Bromine

Calcium

270°
-7°. 3
760°

3
1
2

Carbon (graphite)

3600^

(Diamond)

Chlorine

Chrobhum

-102°

1515°

1100°

-223°

1064°

-257°

114°

1600°

327°

750°

-39°. 4

1450°

-214°

(sublimes)

-33°. 5

1
3:6

Copper

2100°

-187°

1:2

Fluorine

Gold

1
3

Hydrogen

-253°

184°

Iodine

Iron (wrought) .

4.95

7.5
11.3

1.75
13.6

8.8

0.054
0.112
0.031
0.245
0.032
0.109

1
2:3

Lead

Magnesium

Mercury

Nickel

1500°

1100°

357°

7
2

2
2

Nitrogen

-194°

-181°

290°

3:5

Oxygen

Phos- Whitb

44°

1.83
2.16

21.5
0.86
2.5

10.47
0.97
2.07
1.95
7.3
7

0.202

0.17

0.04

0.165

0.181

0.057

0.29

<
PHORUS Red

• • • •

• • • ■

• • • •

3;5

Platinum

1775°
62°.5
White heat
960°
95°.6
114°.5
120°
232°
419°

Potassium

Silicon

Silver

Sodium

720°

Under 3500°

White heat

742°

448°

1600°

930°

1
4
1
1

Sulphur < q

Tin

0.18

0.0562

0.096

• • • •

2;4;6
2;4
2

Zinc :.

12 AN INDUCTIVE CHEMISTRY

IV— SOLUBILITY CURVES FOR 80ME IMPORTANT
SUBSTANCES

£30

10 20 30 40 50 60 70 80
TEMPERATURE CENTIGRADE

Logarithi

Di8.

]

PtaportloBalpArlft

ilL ^

9 |l2 3

5 6

7 8 9

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11 0414

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0253

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17 21 25

29 33 37

0453

0492

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0569

0607

0645

0682

0719

0755 4 8 11

15 19 23

26 30 34

0792

0828

0864

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0934

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1004

1038

1072

1106 3 7 10

14 17 21

24 28 31

1139

1173

1206

1239

1271

1303

1335

1367

1399

1430 3 6 10

13 16 19

23 26 29

1461

1492

1523

1553

1584

1614

1644

1673

1703

1732 3 6

12 15 18

21 24 27

1761

1790

1818

1847

1875

1903

1931

1959

1987

2014 8 6

11 14 17

20 22 25

2041

2068

2095

2122

2148

2176

2201

2227

2253

2279 8 5

U 13 16

18 21 24

2304

2330

2355

2380

2405

2430

2455

2480

2504

2529 2 5

10 12 15

17 20 22

2553

2577

2601

2625

2648

2672

2695

2718

2742

2765 2 5

9 12 14

16 19 21

10 2788 1

2810

2833

2856

2878

2900

2923

2945

2967

2989 2 4

9 11 13

16 18 20

8010

8032

3054

3075

3096

3118

3139

3160

3181

3201 2 4

8 11 13

15 17 19

3222

3248

3268

3284

3304

3324

3345

3865

8385

3404 2 4

8 10 12

14 16 18

3424

3444

3464

8483

3502

3522

3541

3560

3579

3598 2 4

8 10 12

14 15 17

8617

3636

3655

3674

3692

3711

3729

3747

3766

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9 U

18 15 17

8802

3820

3838

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3874

3892

8909

3927

8945

3962

9 11

12 14 16

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4031

4048

4065

4082

4099

4116

4133

2 8

9 10

12 14 15

4150

4166

4183

4200

4216

4232

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4265

4281

4298

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11 13 15

4314

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4425

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8 9

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28 4472

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8 9

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29 4624

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7 9

10 12 13

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4786

4800

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7 9

10 U 13

4914

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4955

4969

4983

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7 8

10 11 12

5051

5065

5079

5092

5105

5119

5132

5145

5159

5172 1 8

7 8

9 1112

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5198

5211

5224

5237

5250

5263

5276

5289

5302

6 8

9 10 12

5815

5828

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5416

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9 10 11

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5490

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4^514

5527

5539

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6 7

9 10 11

5563

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5587

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5623

5685

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£670

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8 10 11

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5694

5705

5717

5729

5740

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5763

5775

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a 9 10

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5809

5821

5832

5843

5855

5866

5877

5888

5899

1 2

6 7

8 9 10

5911

5922

5933

5944

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5966

5977

5988

5999

6010 1 2

5 7

8 9 10

6021

6031

6042

6053

6064

6075

•

6085

6096

6107

6117

1 2

5 6

8 9 10

6128

6188

6149

6160

6170

6180

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6201

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6222

1 2

5 6

7 8 9

6232

6248

6253

6263

6274

6284

6294

6304

6314

6325

1 2

6 6

7 8 9

6885

6345

6355

6365

6375

6385

6395

6405

6415

6425

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5 6

7 8 9

6435

6444

6454

6464

6474

6484

6498

6503

6518

6522

1 2

5 6

7 8 9

6582

6542

6551

6561

6571

6580

6590

6599

6609

6618

5 6

7 8 9

6628

6637

6646

6656

6665

6675

6684

6693

6702

6712

1 2

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7 7 8

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6780

6739

6749

6758

6767

6776

6785

6794

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6 7 8

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6848

6857

6866

6875

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4 5

6 7 8

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6920

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6972

6981

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8 7 8

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6998

7007

7016

7024

7033

7042

7060

7059

7067

4 5

6 7 8

7076

7084

7098

7101

7110

7118

7126

7135

7143

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7168

7177

7185

7193

7202

7210

7218

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7235

1 2

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6 7 7

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7251

7259

7267

7275

7284

7292

7300

7308

7316

1 2

4 5

6 6 7

7824

7832

7840

7848

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7364

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7380

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Mat

8 91

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7490

7497

7606

7513

7520

7528

7536

7643

7651

6 7

7669

7566

7574

7582

7589

7597

7604

7612

7619

7687

6 7

7634

7642

7649

7657

7664

7672

7679

7686

7694

7701

6 7

7709

7716

7723

7731

7738

7745

7762

7760

7767

7774

6 7

7782

7789

7796

7803

7810

7818

7825

7832

7839

7846

6 6

7853

7860

7868

7875

7882

7889

7896

7908

7910

7917

6 6

7924

7931

7938

7945

7952

7959

7966

7973

7980

7987

6 6

7998

8000

8007

8014

8021

8028

8035

8041

8048

8055

6 6

8062

8069

8075

8082

8089

8096

8102

8109

8116

8122

5 6

8129

8136

8142

8149

8156

8162

8169

8176

8182

8189

5 6

8195

8202

8209

8215

8222

8228

8235

8241

8248

8254

5 6

8261

8267

8274

8280

8287

8293

8299

8306

8312

8319

6 6

8325

8331

8338

8344

8351

8357

8363

8870

8376

8382

8388

8395

8401

8407

8414

8420

8426

8432

8489

8445

8451

8457

8463

8470

8476

8482

8488

8494

8500

8506

8513

8519

8525

8531

8537

8543

8549

8555

8561

8567

8573

8579

8585

8591

8597

8603

8609

8615

8621

8627

8683

8689

8645

8651

8657

8663

8669

8675

8681

8686

8692

8698

8704

8710

8716

8722

8727

8733

8739

8746

8751

8756

8762

8768

8774

8779

8785

8791

8797

8802

8808

8814

8820

8825

8831

8887

8842

8848

8864

8859

8865

8871

8876

8882

8887

8898

8899

8904

8910

8915

8921

8927

8932

8938

8943

8949

8954

8960

8965

8971

8976

8982

8987

8993

8998

9004

9009

9015

9020

9025

9031

9036

9042

9047

9053

9058

9063

9069

9074

9079

9085

9090

9096

9101

9106

9112

9117

9122

9128

9133

9138

9143

9149

9154

9159

9165

9170

9176

9180

9186

4 6'

9191

9196

9201

9206

9212

9217

9222

9227

9232

9238

9243

9248

9253

9258

9263

9269

9274

9279

9284

9289

9294

9299

9804

9309

9315

9320

9325

9330

9835

9340

9345

9350

9355

9360

9365

9370

9375

J9380

9335

9390

9395

9400

9405

9410

9415

9420

9425

9430

9435

9440

9445

9450

9455

9460

9465

9469

9474

9479

9484

9489

9494

9499

9504

9509

9513

9518

9523

9528

9533

9538

90 9542

9547

9552

9557

9562

9566

9571

9576

9581

9686

9590

9595

9600

9605

9609

9614

9619

9624

9628

9633

9638

9643

9647

9652

9657

9661

9666

9671

9676

9680

9685

9689

9694

9699

9703

9708

9713

9717

9722

9727

9731

9736

9741

9745

9760

9754

9759

9763

9768

9773

9777

9782

9786

9791

9795

9800

9805

9809

9814

9818

96 9823 1

9827

9832

9836

9841

9845

9850

9854

9859

9863

9868

9872

9877

9881

9886

9890

9894

9899

9903

9908

9912

9917

9921

9926

9930

9934

9939

9943

9948

9952

9956

8961

9965

9969

9974

9978

9983

9987

9991

9996

£_

3 4

9 1

8 9

414

APPENDIX

415

VI— ABUNDANCE OF THE ELEMENTS IN NATURE

List of the Elements in Order of
Abundance.

Composition

of the solid

crust of the

earth.

Composition
of sea-water

Oxygen

Silicon

Aluminium

Iron

Calcium . . .
Magnesium

Sodium

Potassium .
Hydrogen . .
Titanium. .

Carbon

Chlorine . . .
Phosphorus
Manganese .
Sulphur. . .

Barium

Nitrogen . .
Chromium .

Per cent.

47.29
27.21
7.81
5.46
3.77
2.68
2.36
2.40
0.20
0.33
0.22
0.01
0.10
0.08
0.03
0.03
0.01
0.01

Per cent.

85.79

0.05
0.14
1.14
0.04
10.67

2.08

0.09

100 per ct. 100 per ct. 100 per ct

Composition
of the earth's

crust, includ-
ing the ocean

and the at-
mosphere.

Per cent.

49.98
25.30
7.26
5.08
3.51
2.50
2.28
2.23
0.94
0.30
0.21
0.15
0.09
0.07
0.04
0.03
0.02
0.01

The crust of the earth does not contain as much as 0.01 per cent, of
any of the remaining 60 elements. The entire 60 make up but a small
fraction of 1 per cent.

The student should notice the striking inequality in the dis-
tribution of the elements. Two of them, oxygen and silicon,
make up three-quarters of the earth's crust. Native elements
play only an unimportant part in the construction of the planet.

The sun and the stars, comets, and meteors are composed of
the same elements which we find upon the earth. A sample of
magnesium, obtained from a meteor composed of magnesium
silicate, proved to have the same atomic weight as the magnesium
found upon the earth.

INDEX

The topics in bold-faced type are those required by the syllabus of
the College Entrance Examination Board. As a rule, a subject which
occurs several times, under different headings, is printed in bold-faced
tjrpe once only.

Absolute zero, 66.

Acetate, ethyl, 353.
Acetic acid, 201.

constitution of, 353.

properties of, 202.

series, 204.
Acetylene, 183-185.

blowpipe, 185.

burner, 184.

generators, 184.

liquid, 184.

series, 189.

thermochemistry of, 185.
Acid, definition of, 202, 204
Acid, acetic, 201.

boric, 340.

butyric, 204, 354

carbonic, 321.

chloric, 306.

formic, 203.

gallic, 283.

hydrazoic, 173.

hydriodic, 258.

hydrobromic, 262.

hydrochloric, 216-223.

hydrofluoric, 263.

lactic, 323.

nitric, 297-300.

oleic, 355.

palmitic, 204, 354.'

phosphoric, 329.

steanc, 204, 354.

sulphuric, 274-280.
Acids^ action of, on sugar, 195.

active and inactive, 254

conductivity of, 247.

explained in terms of ions,
253.

Acids, general properties of,

202.
Acid-forming elements, 366.
Acid phosphate, 330.
Acid reaction to indicators,

257.
Activity of acids, 202, 247, 254.
Agate, 133.
Air, 48-60.

animals in relation to, 102,
104.

argon of, 59.

carbon dioxide of, 102.

composition of, 49, 55, 57.

density of, 48.

helium of, 60.

history of, 57.

krypton of, 60.

Uquid, 176.

mixture or compoimd, 55

solubiUty of, 73.

water vapor of, 125.

weight of liter of, 48.
Alcohol, ethyl, 197.

denatured, 198.

fermentation, 196, 200.

of crystallization, 326.

oxidation of, 201.

uses of, 197.
Alcohol, methyl, 41, 202.
Alcohol, wood, 41, 202.
Alcoholic liquors, 199.
Aldehyde, ethyl, 200.
Aldehyde, methyl, 202.
Aldehydes, series of, 203.
Ale 199.
All^, definition of, 257.

effect of, on litmus, 246.

INDEX

Alkali, neutralization of, by
adds, 246.

normal, 257.
Alkaloids, 357.

defined, 362.
Allotropic, 40, 47.
Allotropy of carbon, 40.

of oxygen, 320.

of phosphorus, 328.

of sulphur, 4.

of tin, 127.
Alloy defined, 36.
Alloys of aluminium, 130.

of antimony, 334.

of arsenic, 332.

of bismuth, 335.

of cadmium, 335.

of chromium, 342.

of copper, 35.

of gold, 30.

of iron, 145, 146.

of lead, 12, 35.

of magnesium, 131.

of manganese, 132.

of nickel, 35, 342.

of platinum, 34.

of silver, 33.

of tin, 35.

of zinc, 35.
Alloys, brass, 35.

bronze, 35.

coinage, 30, 33, 35.

fusible, 335.

German silver, 35.

gun-metal, 35.

magnalium, 131.

nature of, 35.

pewter, 35.

shrapnel, 334.

solder, 35.

type-metal, 334.
Alluvial defined, 36.
Allylene, 189.
Alum, chrome, 287.

potassium, 287.

sodium, 287.
Alums, general formula for,
287.

Alums, manufacture of, 287.

use of, in dyeing, 287.

use of, in tanning, 287
Aluminium, 129.

alloys of, 130.

bronze, 130.

history of, 131.

metallurgy of, 129.

occurrence of, 128.

oxide of, 128, 129.

price of, 131.

production of, 129.

properties of, 129. "^

silicate, 339.

sulphate, 286.

uses of, 130.
Aluminum, see Aluminium.
Amethyst, 133.
Ammonia, 170-173.

anhydrous, 171, 178.

composition of, 171.

formation of, 172, 173.

ice-making with, 178.

Hquid, 171, 178.

preparation of, 170.

properties of, 171, 172.

uses of, 173.

in water analysis, 172.
Ammonia ice-machine, 178.
Ammonia soda process, 323.
Ammonia water, 170
Ammonium, 238.

carbonate, 323.

chloride, 236-238.

compoimds, 237.

nitrate, 302.

sulphate, 287.

salts, 238.
Amorphous, 2, 8, 9.
Anaesthetics, 235, 354.
Analysis defined, 26.
Analysis, of minerals, 10, 13,
14, 15, 17.

of water, 172.

use of H^S in, 169.
Anhydride, defined, 295.
Animal charcoal, 194.
Anode, 211.

INDEX

Anode, defined, 215.
Anthracene, 186.
Anthracite coal, 45.
Antimony, 334.

alloys of, 334.

compounds of, 334.

trisulphide, 334.
Apatite, 330.
Aqua fortis, 298.
Aqua regia, 300.
Argon, 59.
Aristotle, 51.
Armor plate, 149, 342.
Arsenic, 332.

compounds of, 333.

sublimation of, 332.

uses of, 332.
Arsenic trioxide, see Arsenious

oxide.
Arsenious oxide, 333.

Marsh's test for, 333.

uses of, 333.
Arseno-pyrite, 332.
Arsine, 333.
Artificial diamonds, 38.

graphite, 43.

rubies, 128.

sapphires, 128.

stone, 339.
Ashes of coal, 45.

of plants, 331.

of sea-weed, 260.
Asphalt, 190.
Atmosphere, 48.

animals in relation to, 102,
104.

argon in, 59.

carbon dioxide in, 102.

composition of, 49, 55, 57.

inert gases in, 60.

liquefaction of, 175.

nitrogen in, 51.

oxygen in, 52.

ozone in, 321.

plants in relation to, 104

pressure of, 48.

water vapor in, 125.

weight of, 48.

Atmosphere, see also Air.
Atom, definition of, 166.
Atomic heat, 228.

theory, 154.
Atomic weights, 84-88, 92.

List of, see Table inside rear
cover.

Problems on, 395.
Atoms, 154.

combining power of, 224.

compared with ions, 252.

compared with molecules,
154.

replacement of, 234.

valence of, 224.
Atropine, 357.
Avog^dro's hypothesis, 74.

Bacteria, 178.

on roots of plants, 306.

in vinegar, 201.

in water, 172.
Baking powder, 323.
Baking soda, 322.
Balard, Jerome Antoine, 260.
Barium, 312.

chloride, 275.

nitrate, 312.

oxide, 318.

peroxide, 318.

sulphate, 285.
Barytes, 285.
Base and noble metals, 34,

367.
Base, definition of, 257.

definition in terms of ions,
253.
Bases, conductivity of, 246.

ionization of, 253.

neutralization of, 246.
Base-forming elements, 366.
Basic slag, 147.
Basis of atomic weights, 231.
Battery, storage, 79, 92.
Bauxite, 130, 287.
Becquerel, 345.
Beer 199.
Beetl K2CO3 from, 324.

INDEX

Beet sugar, 194.
Benzene, 183, 185.

source of, 185.

uses of, 186.
Benzine, 187, 188.

composition of, 188.

source of, 188.

uses of, 189.
Bessemer process, 147.

basic, 147.
^ compared with Open Hearth

process, 149.
Bessemer steel, uses of, 147.
Beverages, alcoholic, 199.

effervescent, 98.
Bicarbonate, sodium, 322.
Bismuth, 334.

alloys of, 333.

chloride, 335.

ion, 335.

nitrate, 335.

subnitrate, 335.
Bituminous coal, 45.
Bivalence, 224.

defined, 232.
Black lead, 39.
Blacksmith's scales, 83.
Blasting gelatin, 352.
Bleachkig by cUorine, 318.

by hydrogen peroxide, 319.

by sulphur dioxide, 4.
Bleaching powder, 317.
Blowholes, in ingots, 130.
Blowpipe, acetylene, 185.

oxyhydrogen, 185.

use of, in making Welsbach
mantle, 344.
Bluestone, 280.
Blue vitriol, 280.
Boiler scale, 317.

defined, 326.
Boiling-point of colloidal solu-
tions, 360.

of solutions, 248.

of suspensions, 214.
Bone, phosphorus in, 332.
Boneblack, 194.
Borax, 340.

Bordeaux mixture, 280.
Boric acid, 340.

as food preservative, 341.
Boron, 340.
Boyle, 65.

Boyle's Law, 64, 65.
Brass, 35.
Breathing, changes produced

in air by, 104.
Bricks, 339.

color of, 83.
Brilliant, 47.
Brine, from salt wells, 206.

use of, in refrigeration, 179.
Bromides, 262.
Bromine, 260.

compoimds, 261, 262.

discovery of, 260.

name, 261.

production of, at Stassfurt,
261.

production of, in U. S., 261.

properties of, 261.

uses of, 262.
Bronze, 35.

aluminium, 130.
Bullets for shrapnel, 334.
Burette, 246.
Burner, acetylene, 184.
'^Burning"of lime, 314.
Butane, 187.
Butter, 354.
Butyric acid, 204.
Butyrin, 354.

Cadmium, 143.

oxide, 143.

sulphide, 143.

yellow, 143.
Caesium, 369.
Caffeine, 357.
Calcite, 311-313.
Calcium, 312.

behavior of, with water, 311.

flame color, 262, 311.

preparation of, 311.

properties of, 312.
Calcium carbide, 183.

INDEX

Calcium carbonate, 311-313.

fluoride, 262, 266.

hydrogen phosphate, 330,
331.

hydroxide, 316.

oxide, 313-316.

phosphate, 329-331

sulphate, 284.
Calculations, chemical, 378-

405.
Calomel, 233, 234.
Calorie, defined, 114, 125.
Calx, 36.
Candy, 195, 337.
Cane sugar, 194.
Carat, gold, 30.

diamond, 47.
Carbide, calcium, 183.
Carbohydrates, 195.

defined, 204.
Carbolic acid, 43.
Carbon, 40.

amorphous, 44.

crystallized, 37; 39.

disulphide, 46.

effect of, on iron and steel,
145, 146.

silicide, 134.

suboxide. 111.

tetrachloride, 235.

vapor, 42.

see also Diamond, Graphite,
Lampblack, etc.
Carbonates, 311-326.
Carbon dioxide, 98-105.

composition of, 98-100.

connection of, with life, 102-
104.

detection of, 98.

effect of, on body, 105.

formation of, 99, 101, 102.

importance of, to plants,
103-105.

Hquid, 100.

occurrence of, 101.

of air, 102.

properties of, 100.

solid, 101.
28

Carbon, test for, 98.

uses of, 101.
Carbonic acid, 321.
Carbon monoxide, 105-108.

composition of, 106.

in illuminating gas, 107.

in water gas, 149.

poisonous action of, 106.

preparation of, 203.

properties of, 107.

uses of, 149, 150.
Carborundum, 134.

furnace, 135.

uses of, 135.
Carburetter, 149.
Carnelian, 133.
Cast iron, 145.
Castner process, 245.
Catalysis, 97.
Catalyst, 97.

defined, 111.
Catalytic action, 96, 97.

defined, 111.
Catalyzer, 97.

defined. 111.
Cathode, 211.

defined, 215.
Caustic potash, 245.
Caustic soda, 244.
Celluloid, 352.
Cellulose, 196.

nitrates, 351.
Cement, 339.

defined, 341.
Centimeter defined, 60.
Cerium oxide, 344.
Chalcedony, 133.
Chalcopyrite, 14.
Chalk, 313.
Change, physical, 26.

chemical, 8, 23, 26.
Charcoal, animal, 194.

bone, 194.

conversion into graphite,
42.

wood, 41. •

Charles' law, 66.
Chemical action, 8, 23, 26.

INDEX

Chemical action at high tem-
peratures, 38, 42, 46,
135, 330.

at low temperatures, 265.
Chemical change, 8, 23, 26.
Chemical compounds, 21.
Chemical effects, of electricity,
129, 211, 245, 251, 292.

of heat, 121, 122.

of light, 191, 217, 267.

of moisture, 217, 237, 336.
Chemical energy, 137.
Chemical equations, 91, 92.
Chemical equilibrium, 83. 119,

171, 222.
Chemistry, definition of, 26.

importance of, 26.

name, 26.

task of, 23.
Chili saltpeter, 296.
Chlorates, 305.
Chloric acid, 306.
Chloride of lime see Bleaching

powder.
Chlorides, of metals, 233.

of non-metals, 234.
Chlorine, 211-213.

Deacon's process for, 220.

history of, 212.

Uquid^ 213.

manufacture of, 213, 220.

nitrogen compounds of,
234.

oxides of, 234.

preparation of, 220.

properties of, 212.

uses of, 318.
Chloroform, 235.
Chromates, 343.
Chrome alum, 287.
Chrome green, 342.
Chrome iron ore, 342.
Chrome leather, 342.
Chrome steels, 342.
Chrome yellow, 343.
Chromic ticid, 343.
Chromic oxide, 342
Chromium, 342.

Chromium, preparation of, 342.

properties of, 342.

uses of, 342.
Chromium triozide, 343.
Cinchona tree, 357.
Cinnabar, 15.

Classification of elements, 364-
369.

periodic, 370.
CUy, 338.
Clover, 306.
Coal, 44, 45.

anthracite, 45.

bituminous, 45.

composition of, 44, 45.

destructive distillation of,
43, 181.

fire, 106.

gas, 43, 181.

mines, gases in, 181, 303.

slow and rapid combustion
of, 121.

spontaneous combustion of,
122.

supply of, 45.

uses of, 45.

waste of, 45.
Coal tar, 182, 186.
Coal tar dyes, 186.
Cobalt, 288.

chloride, 289.

nitrate, 289.
Cocaine, 357.
Coffee, 357.
Coins, copper, 35.

gold, 30.

nickel, 35, 36.

silver, 33.
Coke, 43, 181.
CoUodion, 352.
Colloidal. 359.

defined, 362.
Colloidal solutions, 359-363.

defined, 363.
Colored glass, 338.
Colors of solutions, 288, 289.
Combination, chemical, 21.

between gases, 107.

INDEX

Combination by volume, 107.

by weight, 22, 25.
Combustion, 55.

defined, 60.

in coal fire, 122.

in oxygen, 55.

of acetylene, 184.

of hydrocarbonSi 184.

rapid, 120.

reversed, 123, 124.

slow, 121.

spontaneous, 122.

with flame, 122, 123.

without flame, 122, 123.
Common salt, 206.
Compounds, 21, 25.

and elements, 25.

and mixtures, 18-22.
Concentration, 83, 119.

defined, 92.
Conductivity, o* alloys, 36.

of metals, 365.

of solutions, 247.

of water, 290.
Contact action, 97, 111.
Contact process for sulphuric

acid, 274.
Converter, 147.
Copper, 14, 15.

alloys, 35.

glance, 20.

mines near Lake Superior, 15.

native, 15.

occurrence of, 14, 15.

ores, 14.

plating, 282.

production of, 15.

properties of, 14.

pyrite, 14.

refining, 282.

uses, 15.
Copper chloride, 220.

oxides, 81, 82.

sulphate, 280.

sulphide, 20, 84.
Copperas, 283.
Corn starch, 193.
Cordite, 352.

Corrosive sublimate, 233, 234.

Corundum, 128.

Cosmoline, 188.

Courtois, 258.

Cream of tartar, 323.

Creosote, 43.

Critical temperature, 101.

defined. 111.
Crockery, 339.
Crucible steel, 146.
Cryolite, 129, 266.
Crystal, definition of, 9.

rock, 133.
Crystallization, water of, 281,

326.
Crystalloids, 359.

defined, 363.
Cube, 10, 26.
Cubical cleavage, 10.
Cubic centimeter, defined, 60.
Cupric chloride, 220.

oxide, 81, 82.

sulphate, 280.

sulphide, 84.
Cuprite, 82.
Cuprous oxide, 81, 82.

sulphide, 20.
Curie, 345, 346.
"Curve," defined, 214.
Cyanide, potassium, 29.

sodium, 210.
Cyanide process, 29.

Dalton, 165.
Davy, 212, 245, 303.
Deacon's process for chlorine,

220.
Decompose, defined, 60.
Definite proportions, law of,

25, 164.
Deliquescence, 325.

defined, 326.
Democritus, 165.
Denatured alcohol, 198
Density, defined, 75.
Deposit, defined, 9.
Destructive distillation, 43,

181.

INDEX

Determination of atomic

weights, 226-231.
Detonation, 352.
Developer, 268.

defined, 270.
DeviUe, 131.
Dewar, 177.

Dewar vacuum vessel, 176.
Dextrin, 327.
Dialvzer, 359.
Diamond, 37-39.

artificial, 38, 39.

black, 39.

combustion of, 98.

conversion of, into graphite,
40.

Cullinan, 39.

Kimberley mines, 37.

Moissan's experiments on,
38.

uses of, 38.
Diastase, 198.
Dichromates, '342.
Diffusion, 63.

due to molecular motion, 68.

in gases. 63.

in Rquias, 63.

in solids, 63.
Direct current defined, 216.
Disinfectants, 43, 95, 202, 234,

283.
Dissociation, defined, 240.

of calcium carbonate, 314.

of sal-ammoniac, 237.
Distillation, defined, 125

destructive, 181.

of alcohol, 197.

of coal, 43, 181.

of nitric acid, 297.

of petroleum, 188.

of water, 112, 113.

of wood, 41.
Distilled liquors, 199.

water, 113, 290.
Double refraction, 311.
Drying of gases, 336.
Ductile, defined, 36.
Ductility of metals, 365.

Dulong and Petit, 228.
Dutch process for white lead,

325.
Dynamite, earth, 351.
gelatin, 353.

Earthenware, 339.
Efflorescence, 326.

defined, 326.
Electric furnace, 136.

arc type of, 136.

carbon disulphide in, 46.

carborundum, 135.

electrodes in, 40.

Moissan's work with, 38, 42.

phosphorus in, 330.

resistance type of, 136.

steel and the, 136.

temperature of, 136.
Electric light carbons, for

flaming arc, 262.
Electrical conductivity,
of acids, 254.

of alloys, 36.

of bases, 246.

of metals, 365.

of salts, 251.

of solutions, 247.
Electrode, 211.

defined, 215.
Electrolysis, defined, 257.

of aluminium oxide, 129.

of copper sulphate, 281.

of hydrochloric acid, 222.

of potassium chloride, 213.

of potassium hydroxide, 245.

of sodium chloride, 211.

of sodium hydroxide, 245.

of sodium sulphate, 292.

of sulphuric acid, 293.

of water, 292.

theory of, 251, 252.
Electrolytes, 247.

defined, 257.
Electrolytic copper, 282.
Electrolytic, process for alu-
minium, 129.

process for calcium, 311.

INDEX

Electrolytic, process for chlo-
rine, 213.
process for potassium, 245.
process for sodium, 245.
Electrolytic purification of
copper, 282.
of gold, 299.
of silver, 299.
Electromotive series, 293.
Electro-negative elements, 366.

ions, 366.
Electro-positive elements, 366.

ions, 366.
Electrons, 362, 370.

defined, 363.
Electro-plating, 282.
Electro-typing, 282.
Element, defined, 24, 25.
Elements, abundance of, in na-
ture, see Appendix, Table
VI.
acid-forming, 366.
base-forming, 366. '
classification of, 364-377.
families of, 368.
in earth's crust, see Appen-
dix, Table VI.
in living matter, 358.
occurrence of, see Appen-
dix, Table VI.
periodic arrangement of,

374.
prediction of, 375.
radio-active change of, 348.
rare, uses of, 89, 344.
table of atomic weights of,
see Table inside rear
cover.
Emerald, 339.
Emery, 128.
Emulsion, 269.
defined, 271.
Endothermic reactions, 139.
Energy, chemical, 137-139.
chemical, importance of , 137.
chemical, measurement of,

138.
chemical, uses of, 137.

Energy of coal, 45.

of explosives, 302.

of life, 192.
Epsom salt, 285.
Equation, chemical, 91, 92.

ionic, 255.

molecular, 159.

thermochemical, 138.

use of, in solving problems,
91, 92.
Equivalent weights, 86.
Erosion of calcium carbonate,

313.
Esters, defined, 240.

of carbon acids, 353.
Etching, of glass, 263.
Ethane, 187.
Ether, 354.

defined, 362.
Ethyl acetate, 353.

alcohol, 197.

ether, 354.

oxide, 354.
Ethylene, 183, 189.
Evaporation, 124, 125.
Eudiometer, 108, 117.
Exothermic reactions, 139.
Explosives, 301, 350-353.
Exposure, photographic, 269.

False topaz, 133.
Families of elements, 368.
Faraday, 174, 251.

tube, 174.
Fats, 354.
Felspar, 339.
Fermentation, 196.

acetic, 201.

alcoholic, 196.

defined, 204.

without yeast-cells, 200.
Ferric oxide, 82.
Ferro-manganese, 132.
Ferrous sulphate, 283.

sulphide, 79.
Fertilizer, 331.

elements essential in, 331.

from air, 308, 309

1 10

INDEX

Fertiliier, nitrate, 296, 308.

Ditro-lime, 309.

phosphate, 331.

potassium, 242, 339.

superphosphate, 331.
Filament, defined, 47.
Film, photographic, 269.
Filtration of solutions, 214.

of suspensions, 214.
"Fire air," 58.
Fire-damp, 181.
Fire extmguisher, chemical,

322.
Fischer, Emil, 359.
Fixing, photographic, 269.

defined, 271.
Flame, defined, 125.

acetylene, 184, 185.

air, 124.

hydrogen, 123.

oxy-acetylene, 185.

oxygen, 124.

oxy-hydrogen, 123.

test, 209, 215.
Flaming arc lamp, 270.
Flash-light powder, 285.
Flavoring esters, 354.
Flint, 133.
Flour, 191.
Fluoride, calcium, 262, 266.

hydrogen, 263.

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